GMC Sierra 2500HD AT4 — Turbo diesel performance

By Jim Meachen and Ted Biederman

If your goal is to make the biggest statement possible in terms of performance, off-roading, towing, payload, interior refinement and advanced technologies all in one truck look no further than your nearest GMC dealer. Check out the 2021 off-road-ready GMC Sierra 2500HD AT4 Crew Cab with the 6.6-liter Duramax turbo diesel V-8 paired to a 10-speed Allison automatic transmission.

The numbers speak to this truck's capabilities. And once behind the wheel, the big GMC's driving demeanor will be the clincher. That's if you don't mind letting loose of $69,885. That number includes a whopping $9,890 for the diesel engine.

It's a big price to pay, but you get big things in return. For instance towing capacity is 18,500 pounds — not best in class, but prodigious all the same. You can load the bed up with the stuff of your work or play with up to 3,597 pounds. Note that if towing capacity is your primary concern, the Sierra 3500 HD with max tow package has a rating as high as 36,000 pounds.

Perhaps best of all for daily driving is the performance produced by the big diesel. It's tasked with propelling the 7,700-pound truck in an expeditious manner and it succeeds with 445 horsepower and a massive 910 pound-feet of torque available. Performance has been measured at 7.1 seconds from 0-to-60, which can be translated into plenty of grunt. We didn't tow anything during our test and never had more than four people and no additional payload. In that configuration the truck's performance proved satisfying.

We can't speak to the diesel's fuel economy because an EPA gas-mileage rating is not required. But we do know that mileage is better than on the comparable GM 6.6-liter V8 gas engine, and regardless of its mpg the truck's 36-gallon tank should alleviate the need for frequent fuel stops. Just be ready to dig deep into the pocketbook when a service station visit is required.

The AT4 designation brings a higher ride height and dynamic styling cues that create a more aggressive and bolder appearance. AT4 adds an off-road suspension with Rancho shocks, skid plates, and all-terrain tires for rugged off-roading. Additionally, you get GMC's six-function MultiPro tailgate which is reconfigurable into six different positions. GMC calls the pickup tailgate the most innovative ever, offering enhanced second-tier loading, a standing workstation, and easy access to items in the box.

Our test truck also came with the AT4 Premium Package for $7,975, which includes a plethora of equipment including several cameras that are invaluable in tight parking lot situations. The package also brings numerous safety devices including a blindspot monitor with cross-traffic alert — something we think should be standard equipment. A power sunroof and a Bose premium audio system are also included.

We like the new GM truck's interior, although it has been criticized as having a dated look. Maybe we are out of step, but we like the "dated look" with big knobs and easy-to-use switchgear. The layout is simple and intuitive and we think just right for a working truck. The center console is huge with considerable storage, and a dual glovebox also aids in storing stuff.

Every Sierra HD comes with an 8-inch touchscreen that features Chevy's Infotainment3 software, which includes standard Apple CarPlay and Android Auto.  We concede that the touchscreen is not as big as some competitors and can't compete with the "wow" factor of the big tablet layout found in Ram trucks, but it is big enough and it looks nice, flowing neatly into the dashboard layout.

The AT4 shines on the highway with a smoother ride than we had anticipated from its off-road chops, quiet at highway speeds, and easy to direct down the road with accurate steering. Interior space in the Sierra is huge and rear-seat passengers in the crew cab truck can truly stretch out. And there's comfortable room for three in the second row. The downside to the AT4 is it’s around two-inch extra ride height, which makes entering and exiting for older, tired bodies somewhat of a chore. We carried a foldable step-stool for one of our shorter passengers.

Other than AT4, the Sierra 2500HD comes in four other trim levels — Base, SLE, SLT and Denali. The AT4, which was added to the lineup for 2020, falls just below the luxury-infused Denali. The base 2500HD starts at $40,100 in regular cab configuration and $44,170 for the crew cab. The SEL crew cab starting at $49,590 might be the sweet spot for the most equipment for the money.

The AT4 crew cab starts at $59,995 including destination with the standard 6.6-liter V-8 gas engine and the Denali at $66,495. Our diesel AT4 with options carried a bottom line of $78,050.

2021 GMC Sierra 2500HD diesel


Base price: $44,170; as driven, $78,050
Engine: 6.6-liter turbo V-8 diesel
Horsepower: 445 @ 2,800 rpm
Torque: 910 @ 1,600 rpm
Transmission: 10-speed automatic
Drive: four wheel
Seating: 2/3
Wheelbase: 158.94 inches
Length: 250 inches
Curb weight: 7,721 pounds
Turning circle: NA
Towing capacity: 18,500 pounds
Fuel capacity: 36 gallons (diesel)
EPA rating: NA
0-60: 7.1 seconds (Car and Driver)
Also consider: Ford F-150 Super Duty, Ram 2500HD

The Good
• Powerful diesel engine
• Large towing, hauling capabilities
• Variety of available models

The Bad
• Too much safety tech is optional

The Ugly
• Hard to maneuver in tight spaces