2021 GMC Sierra 2500HD

By December 30, 2020

The 2021 GMC Sierra Heavy Duty is the uptown cousin of the Chevrolet Silverado HD. It was updated last year, and for 2021 it gets two new models, one for off-road (X31) and another for luxury (Denali Black Diamond). It comes in 2500 and 3500 versions, with single- or dual-rear-wheel configurations, and a choice of two V-8 engines, standard or turbodiesel. Regular-, double-, or crew-cab configurations are available, the last of which is most popular.

Probably even more than other trucks in its class, the Sierra is all about size, at least from a visual standpoint, with its hugely wide and tall grille, and body sides that are equally imposing in their length and mass.

The standard 6.6-liter V-8 makes 401 horsepower, mated to a 6-speed automatic transmission, and can carry more than 6,000 pounds in the bed. The other engine, a 6.6-liter V-8 turbodiesel, makes an astounding 910 pound-feet of torque to go with its 445 hp. That enables it to tow up to 35,500 pounds. It’s quite expensive, so practically speaking, it’s only useful if you commonly haul heavy trailers, for example full of racecars or horses. It uses a smooth 10-speed automatic transmission. Good thing.

The common crew cabs are very comfortable places to be for up to five adults. GMC offers short or long beds (except regular-cab pickups, which only offer a long bed), that are deep and wide, with a trick tailgate on most models.

It’s not unheard-of for trucks of this size to get city fuel economy in the single digits; out on the highway, the Sierra HD can settle into a lope in the high teens, when there’s no trailer attached. Crew-cab models have a 36-gallon fuel tank that at least extends the range.

The EPA and the NHTSA don’t subject these trucks to testing. The Sierra doesn’t have features such as automatic emergency braking.

Model Lineup

The Sierra HD is offered in base, SLE, SLT, AT4, Denali and X31 models, starting at about $42,000 and climbing past $80,000. With the cab and bed choices, there are too many configurations to list. The Sierra HD is available in regular-, double-, or crew-cab configurations with a short or long bed, in rear-wheel or four-wheel drive.

The Sierra SLE with standard rear-wheel drive is what you get for $42,000, and it’s a stripped-down work truck.

The 2500 HD SLT with the standard V-8 and four-wheel drive costs about $58,000 and includes leather upholstery, heated front seats, an 8.0-inch touchscreen for infotainment with Apple CarPlay and Android Auto compatibility, four USB ports, Bluetooth, 18-inch wheels. Many options are available, including paint, wheels, and eight cameras providing 15 views to help a driver guide the truck into a tight parking space, hitch a trailer, or back a boat into the lake.

Sierra AT4 and Denali editions are for buyers with deep pockets looking for a tough or tony heavy-duty pickup, respectively.

For 2021, the Denali Black Diamond edition adds premium audio by Kicker and 20-inch wheels; a Sierra HD X31 version is a more affordable off-road model.


The 2021 GMC Sierra HD is a brute. It’s more than 22 feet long, can weigh as much as four tons, and has massive shoulders and giant grille framed by sharp LED headlights and a bulging hood scoop. The chrome on the front bumper alone must weigh a ton. The sides of the Sierra HD are mostly flat, although the bottoms tuck in to give it a slightly trim look.


In contrast to the exterior, the interior is plain. Its 8.0-inch touchscreen nearly gets lost in the huge dash. The storage possibilities in the cabin, especially with the Crew Cab, are many. There’s a deep, wide center console with USB chargers, storage compartments in the seats, and more storage under the rear seats.

Up to five people fit in crew-cab models in supreme comfort. The front seats are wide and accommodating, and there’s more than 43 inches of leg room in the rear.

There are two bed sizes. Regular cabs get an 8-foot bed, while double and crew cabs get either an 8-foot bed or a shorter 6-foot-6 bed. Both beds are deep and wide, able to swallow a stack of 4-by-8 sheets of plywood. The beds have 12 tie-downs and a 120-volt power outlet. Many Sierra models come with a six-way folding tailgate with a drop-down section that functions as a step.

Driving Impressions

Two bruising engines offer mighty capability in the 2021 GMC Sierra Heavy Duty pickups. The 6.6-liter gas-powered V-8 makes 401 hp and 464 lb-ft of torque. It can carry a payload of 4,354 pounds with two rear wheels, or 7,442 pounds as a dually, with four rear wheels. It’s mated to a 6-speed automatic transmission.

The 6.6-liter V-8 turbodiesel is for towing. Despite costing about $9,000 more, GMC says that the turbodiesel makes up nearly half of all Sierra sales. The engine makes 445 hp and 910 lb-ft of torque, and can haul a fifth-wheel trailer up to 35,500 pounds, or a conventional trailer up to 20,000 pounds with supreme confidence, attached by a heavy-duty hitch. The turbodiesel is mated to a smooth 10-speed automatic transmission that’s well-suited for long hauls.

Rear-wheel drive is standard, with four-wheel drive available. Two rear axle ratios are available, and the turbodiesel V-8 is available with an integrated power take-off for power machinery such as farm equipment.

Like any big truck, the GMC Sierra HD is a handful around town. Its sheer size makes it difficult to maneuver, although the variable-ratio steering rack helps somewhat. The Sierra HD uses an independent front suspension that’s geared toward ride comfort, which many rivals don’t bother with. Still, when there’s no load in back, the ride is choppy.

Final Word

If you’ve got the scratch, and need the ability to move small mountains, the 2021 GMC Sierra HD is a contender. The Sierra’s big V-8 engines are awesome, while the 10-speed transmission that’s mated to the expensive turbodiesel is better than the 6-speed with the gas V-8.


—by Sam Moses with driving impressions by The Car Connection

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