2015 GMC Sierra HD

By G.R. Whale March 5, 2014

The GMC Sierra HD rolls into the 2015 model year looking like a new truck: The 2015 GMC Sierra HD gets new sheetmetal, a new cab, and interior and infotainment systems that debuted on the light-duty 2014 Sierra 1500. A Sierra Double Cab with four conventional doors replaces last year’s extended cab, and all are roomier. What’s underneath isn’t necessarily new, but evolutionary updating or proven components.

GMC Sierra HD heavy-duty pickups are well suited to real-world use and abuse. They can haul tons of brick and cement and tow the concrete pump, then turn around to be used for a night on the town or grocery shopping while the fifth-wheel’s left in camp or the horses are in the corral. If your hauling is lighter and happens once or twice a year or you tow a bass boat or ski boat, then the 1500-series may be better suited. If your load is heavy, however, or you do a lot of towing, the Sierra HD is the ticket, especially with the diesel engine. We found it towed a 5000-pound trailer load like it wasn’t there and a 15,000-pound trailer with ease.

The luxurious Denali model is available in both 2500 and 3500 models. The 2015 GMC Sierra HD Denali comes standard with heated and cooled front seats, leather-wrapped heated steering wheel and a reconfigurable instrument panel, among other things. Denali is GM’s response to Ford’s King Ranch or Platinum and Ram’s Lariat Longhorn. And Denali gives the GM HD owner a unique choice Chevrolet doesn’t offer.

The 2015 GMC Sierra HD is built on the same chassis as the 2015 Chevrolet Silverado HD and shares all sheetmetal with it. Different hood trim, lights, grille, wheels, ruby red badges and red cabin illumination highlights (rather than aqua) distinguish the GMC from the Chevrolet.

For 2015, Sierra HD adds more standard equipment, like a locking tailgate, cruise control integrated diesel exhaust braking, electronic stability control and trailer sway control across the line. Updated infotainment systems will be available fall 2014 to turn your truck into a Wi-Fi hotspot. Additionally, Sierra HD carries GMC’s Pro Grade Protection that covers scheduled maintenance (including diesel exhaust fluid, oil changes and tire rotations) for 2 years or 24,000 miles.

As with all heavy-duty pickup lines, the 2015 Sierra HD offers plenty of configurations with three cab styles, two bed sizes, single or dual-rear wheels and 2WD or 4WD. A 6.0-liter gasoline V8 is standard, rated at 360 horsepower for all pickup bodies. Power ratings aren’t as high as the competition’s gasoline engines. It’s also offered to run on CNG, dropping power ratings to 301 hp and 333 lb-ft.

The 6.6-liter turbodiesel with 765 pound-feet of torque (more than twice the gas engine’s) is competitive with Ford’s Super Duty at 400 hp and 800 lb-ft and Ram’s 350-385 hp and 660-850 lb-ft. GM and Ford use 6-speed automatics in their trucks; Ram offers a choice of 6-speed automatic or 6-speed manual.

For the entry price you get a functional pickup with load-carrying ability, but for big towing expect to pay much more. Options can add up quickly, with the diesel engine ($7195) and its required transmission upgrade ($1200) among the most expensive, but the tow rating improves in some cases by almost five tons.

The trick in buying the right GMC Sierra HD is to give fair consideration and choose wisely. Compute the permutations among three cabs, two weight classes, two beds, two engine/transmission combinations, two drive systems and four trim levels, and then sort out options that cover everything from a diesel radiator cover to rear park assist, and you can see why prices can more than double from the baseline.

Model Lineup

The 2015 GMC Sierra HD offers three cabs, two beds, five wheelbases, rear or four-wheel drive and four trim levels. The Vortec 6.0-liter V8 and 6-speed automatic comes standard, the Duramax diesel with a stronger Allison 6-speed automatic is optional ($8,395) on almost all of them. Regular Cabs and most 3500 are long bed (8-foot) only, 2500 four-doors are standard (6.5-foot) or long bed; Crew Cab 3500 offers standard bed or long bed. From the least expensive version, each step up in cab size costs $3000-$5000, a long bed about $200 more than a 6-foot, 6-inch version, while four-wheel drive is approximately $3,000.

Sierra HD WT models are work trucks with vinyl upholstery, rubberized floor covering, black door handles and mirrors, steel wheels and floor-shift for 4WD. They come with air conditioning, AM/FM stereo, 2 USB ports and MP3 jack, EZ lift/lower locking tailgate, cruise control, driver information center, 40/20/40 manual-recline front seats, rear bench seat, tilt wheel, chrome grille and bumpers, tow hooks, intermittent wipers, and dual dash power outlets. The WT Crew Cab has a 60/40-split rear bench seat. Options on WT include cloth upholstery, stereo upgrades (XM, Pandora, SD slot, Bluetooth streaming and voice recognition), OnStar Directions & Connections (six months service trial), 18-inch wheels, camper mirrors, locking differential, trailering equipment, integrated trailer brake controller and deep-tint glass.

Sierra HD SLE versions improve with cloth 40/20/40 split bench seat with storage beneath, carpeting (though the WT floor is available), split-fold rear seat, 8-inch IntelliLink touchscreen with gesture recognition, OnStar with six months’ service, cruise control, aluminum wheels, power heated mirrors/windows/door locks, visor vanity mirror/lights and electric-shift for 4WD. SLE options include heated buckets seats, leather upholstery, dual-zone climate control, navigation and backup camera, power sliding rear window, power heated camper mirrors, 20-inch wheels for single-rear wheel trucks, locking differential and Z71 off-road package.

Sierra HD SLT upgrades with leather, 10-way power heated front seats and two-person driver memory, dual-zone climate control, fog lamps, paint-matched trim, power folding mirrors w/signals, 18-inch polished forged aluminum wheels, locking differential, trailer equipment and integrated trailer brake controller. SLT-level upgrades include navigation and rearview camera, Bose audio system, rear-seat entertainment, moonroof, power sliding rear window, power heated camper mirrors, and 20-inch wheels.

Sierra HD Denali models get a unique grille, instrument panel, interior and exterior detailing, body-color bumpers, polished forged aluminum wheels, and EZ-Lift locking tailgate. Inside, Denali adds heated steering wheel, heated and cooled front seats, IntelliLink navigation, 5 USB ports, SD slot, power adjustable pedals, driver memory system, tilt/telescope leather wheel with audio controls, 110-VAC outlet, rear camera, front/rear park assist, fog lamps, locking differential, trailering equipment, trailer brake controller, LED box lighting, chrome side, power defrosted sliding rear window and Bose audio system. Options include the diesel engine, moonroof, driver alert system (forward collision and lane departure warnings), polished aluminum wheels on duallys, and rear-seat entertainment.

Options include spray-on bedliner, bed covers, roof marker lamps, chrome tow hooks, larger or dual alternators, side steps, power heated camper mirrors, LED box lighting, block heater, snow-plow prep for 4WD, high-idle switch, radiator cover and camper/fifth-wheel wiring.

Safety features include frontal airbags, front-side airbags and front side-curtain airbags (on 2500), front seat belt pretensioners, six months OnStar Directions & Connections, electronic stability with trailer sway control and tire-pressure monitors on 2500. Safety related options include front-side airbags and front side-curtain airbags (3500), forward collision alert, lane departure warning, park sensors, backup camera and integrated trailer brake controller.

Walkaround

GMC Sierra HD shares its mechanical bits with the Chevrolet Silverado HD, but they are not visually identical. Different grilles, lights, trim, wheels and badges distinguish the two. Denali models use unique elements of those distinctive parts to further separate themselves from lesser Sierra HDs.

A giant ruby red GMC logo makes Sierra's origin obvious. There's a more obvious gap between bumper and grille that on the light-duty Sierras, and the cooling apertures are greater for higher power loads. Even the duallys have airdams for fuel economy, so angle of approach is lower and more likely to scuff on hills and trail obstacles. Although Denali models are so badged on the doors, it's the huge eggcrate grille and double-dipped-in-chrome look that set it apart most.

New mid-size Double cab models have conventional rear doors. These have myriad advantages over opposite-swinging doors such as those found on extended cabs, including a more rigid cab structure, more roof-crush resistance, quieter, no unlocking belts or doors for those in front. The one disadvantage is that it's not so easy to load awkward items in back. We'll happily take the advantages.

The box sides are deep on the Sierra HD. The tailgate locks and is assisted to open and close with one hand: GM says it weighs about 45 pounds if you remove it for fifth-wheel or gooseneck use. Cargo management equipment includes spray-in and drop-in bedliners, various covers, under-rail LED box lighting, nine upper tie-down points (rated 250 pounds each). The frame is ready for a fifth-wheel hitch, so you'll have to do the holes in the bed.

Most heavy-duty pickups have external dimensions close to each other and the Sierra is similar; more than six-and-a-half feet wide outside with room for a 4×8-foot sheet of building material to ride flat in the long bed. 4WD Sierra HD models ride slightly lower than do Ram HD and Ford Super Duty pickups, and that inch or two could make the difference in commercial garages or with critical fifth-wheel trailer/bed side clearances. On the other hand, it's easier to climb in and out of the cab or load or unload cargo from the bed.

Interior Features

There are only minimal differences between Silverado HD and Sierra HD (non-Denali) interiors: steering wheel logos, some gauge graphics and GMC's red accent lighting in pace of Chevy's aqua array. There's even less difference between Sierra 1500 and HD: gauge values (diesels get unique tachometer and oil pressure gradations) and some switches under the climate controls.

Regardless of cab style, room is appropriate. Regular Cabs are clearly full-size, and the center seat position is useful for those with shorter legs to clear the hump and dashboard. Many of the 40/20/40 bench arrangements that are available have a locking storage area underneath. Also, the center backrest folds for another storage bin.

Crew cab rear doors are larger than before and, except for measured hip room, both Double Cab and Crew Cab have more room than before. The seat cushion, in one section or two, folds up easily for extra interior cargo volume. There's plenty of space in a Crew, competitive with Super Duty and Ram crew cabs, and installing a child seat is hassle-free, but the pint-size rear headrests are a let-down.

The basic dash layout is the same across all 2015 Sierra HD models, though stitched and padded on top for the fancy versions. All have a dual glovebox. A touchscreen (3.5, 4.2 or 8-inch) in the center groups controls for audio/infotainment, climate and ancillary controls (pedal adjust, exhaust brake, bed lights) along the bottom.

Gauges are complete, responsive and easy to read, with more info available in the center of them as dialed up by steering wheel buttons. On Denali, everything between tach and speed is a screen, with representations of gauges along the top. You can configure much of it to taste, and while those gauges can't be changed, selecting Tow/Haul mode automatically swaps out voltmeter for transmission fluid temperature.

To the left are light controls, 4WD switching (with neutral), and the integrated trailer brake controller (when equipped). Since we usually adjust the brake controller while watching the mirrors for trailer tire lockup, this is a handy location.

Materials in the 2015 Sierra HD are a step up from pre-2015 models. If there were any fit/finish issues we couldn't find them, and we've generated our share of complaints. The woodgrain trim isn't real, but aluminum on Denali is.

The high-line Sierra SLT cabin feels just like the interior of a large luxury car, with a low-profile dash sporting lots of woodgrain trim, a compact instrument cluster with good gauges, three months of XM radio to get you hooked, and a center stack that rolls off the dash and right into a full-length center console.

IntelliLink is GMC's moniker for infotainment, like Ram's Uconnect, Chevy's MyLink and Ford's MyFord/sync systems, and we think it works better than the latter. Beyond all the apps, 3-D like mapping and things you can do with it, it has gesture-control and voice recognition for easiest operation and 30 tabs you can assign to radio stations, phone numbers or destinations.

There's plenty of connectivity, with multiple power points, five USB ports, SD card lot, Bluetooth and 4G LTE coming to make your pickup a Wi-Fi hotspot. Models with rear-seat entertainment add another USB and SD port, AC outlet, and video inputs.

All Sierra HD are automatics with a column shift lever. The Tow/Haul mode switch on the end and a +/- rocker on the handle allows manual gear selection after you've moved the lever from D to M. Ford uses a similar arrangement, Ram just a rocker that doesn't first require a lever movement.

Driving Impressions

Since the major mechanical bits are the same, the 2015 Sierra HD drives much like last year’s model, the biggest difference is that it’s much quieter. It didn’t gain any power and only nominal weight, aero is slightly better, so performance remains intact.

At the moment, Sierra HD and Silverado HD lay claim to the highest payload rating for a 3500-series pickup truck at 7374 pounds. However, Einstein would yawn at this since everything is relative and it’s best by less than one percent. Their top tow rating of 19,600 pounds for conventional trailers is about half-a-ton ahead of the competition, while the top fifth-wheel/gooseneck rating is 600-6800 pounds behind the other guys’ best numbers.

Key here is that unless your pulling the maximum fifth-wheel, it doesn’t really matter. Getting to the top of a long grade 15 second behind another guy could be made up at a fuel island because your truck is lighter. Only wacky Brits on television race heavily loaded campers, and only television and YouTube videos race identical trucks and trailers up hill. Also remember not everyone’s best number applies to the same kind of truck, and no pickup is rated carry its max weight and tow its max trailer simultaneously. Bottom line: Don’t choose your brand based on claims. Buy the truck you want.

Where the GMC Sierra feels better than its counterparts is in its relatively quiet, smooth ride and more accurate, direct steering feel.

Note that the Double cab and Crew cab have more advanced body mounts than the regular cab, along with a longer wheelbase, both of which aid ride quality. Alone in 4WD and in a more-refined approach for 2WD pickups, GM uses independent front suspension for its heavy duty pickups, so the front of their truck handles and feels more like a car than the other guys. On the downside it may require realignment after a snowplow or camper is fitted, might cost more to modify if you lift your truck, and it makes the back end, especially on duallys, feel like a rougher ride. It isn’t really, but the front-end absorbs bumps so well you fell it more when the big rear axle hits the same bump a fraction of a second later.

There’s heft to the feel of a Sierra HD, from the way it takes big bumps to steering and throttle inputs, but this should not be construed as effort on the driver’s part. Its handling characteristics are benign and amount to basic plowing if you push too hard. All-terrain tires give better grip on dirt roads at the expense of steering precision and noise on paved roads. Optional 20-inch wheels look good, but we prefer 17- and 18-inch wheels for numerous reasons, including ride quality and replacement cost.

Big parts underneath haven’t changed since the 2011 redesign, but suspensions have been recalibrated for the new cabs, and weight ratings and electronics are updated, and electronic stability control and trailer sway control come standard, even on duallys. We can’t find fault with how any of it works on the road and it acquits itself admirably even if peak torque for the diesel is rated 5-percent less than that of the competitors. Indeed, the Sierra HD often weighs that much less than a comparable competitor.

We got short drive opportunities with various trailer sizes behind 4WD 2500 and 3500 dually diesels. Our experience showed about 14.5 mpg in an empty dually over mountain two-lanes and interstate travel at better than 90 mph, and exactly the same mileage for a single-rear Crew diesel pulling a 5500-pound racecar trailer at more moderate speeds. We also dragged a travel trailer around behind a single-rear Crew gas engine, at 5000 feet elevation, and while it clearly didn’t go like the diesel (and got 8 mpg) we never felt uncomfortable. If in your job or recreation you only infrequently tow a trailer of less than 8000 pounds, and run only 10,000 to 15,000 miles per year total, the gas engine may make more sense.

Buyers who tow many miles should strongly consider the diesel, which delivers twice the torque output and notably better fuel mileage and work ratings. The Duramax diesel is relatively quiet. As with all heavy-duty trucks, the Duramax uses DEF for the emissions system. This is filled underhood and may need to be done only at service intervals but is available at fuel depots and parts stores if you drive hard, drive through hot weather or idle excessively. Running out will not stop the truck, but if you ignore warning messages it eventually be limited to very low speeds.

Both 6-speed automatics offer a Tow/Haul mode that will execute downshifts with throttle blipping to maximize engine braking. In most cases Tow/Haul is designed for optimum use with loads of 70 percent or more of maximum GCWR, though you won’t hurt anything by using it with lighter trailers or not using it with heavier trailers. The diesel exhaust brake works with the cruise control so you may, in theory, never need to use your feet to cross the Rockies.

New lane departure and forward collision alert systems work as elsewhere. In multiple trucks we got one false alarm, forward collision warning of an oncoming truck in the opposing lane on a gentle bend. Note that many of these and other assist systems on any vehicle are dependent on weather, dirt or snow buildup.

A rearview camera is included on some models, a boon for near-in vision and hitching trailers solo. Necessarily a wide-angle device it doesn’t help backing low trailers you can’t see in the mirrors, but we’d still get one. We’d also get the integrated trailer brake controller if for no more than it is warranteed with the truck and enhances resale value. It works better than most you can buy and install yourself.

Summary

Any GMC Sierra HD will get the work done, and the plainer the truck the more it will carry or tow. At the other extreme, the Denali brings Cadillac luxury and current electronics to upgrade working-class trucks to business-class comfort, still able to haul around at least 2900 pounds and tow 13,000 pounds.

G.R. Whale filed this report to NewCarTestDrive.com from Carerfree, Arizona.