2020 GMC Sierra 2500 Diesel Road Test and Review

2020 GMC Sierra HD AT4 White Off Road ・ Photo by GMC

GMC has completely redesigned its heavy-duty line of pickups this year. The brand has been in the truck business for over 100 years, and the 2020 GMC Sierra 2500 is the culmination of that extensive experience. “The all-new 2020 Sierra Heavy Duty is the most capable heavy-duty truck that we’ve ever offered,” says Duncan Aldred, vice president of Global GMC.

Part of the Sierra HD’s makeover is an all-new 6.6-liter V8 gas engine rated to produce 401 horsepower. It’s an impressive powerplant, mated to a smooth and time-tested six-speed automatic transmission. However, for this test, we ordered up a truck with the revised version of GMC’s proven Duramax 6.6-liter turbodiesel, which is now rated to produce 445 horsepower and 910 lb-ft of torque. It’s also paired with the brand’s new 10-speed automatic. With this combination, the GMC Sierra 2500 competes with diesel-powered versions of the Ford F-250, Ram 2500, and its mechanical twin, the Chevrolet Silverado 2500.

Many Models to Choose From

An acronym for General Motor Truck Company, GMC is part of General Motors along with Chevrolet, Buick, and Cadillac. The 2020 GMC Sierra 2500HD and 3500HD are some of the best-selling heavy-duty full-size pickups in the country, and they’re built in Flint, Michigan, on the same assembly line as the similar Chevrolet Silverado 2500HD and 3500HD models.

Five body styles are offered, including regular cab, double cab, and crew cab, and they are all available with four-wheel drive. There are also many trim levels to choose among, including SLE, SLT, and the top-of-the-line AT4 and Denali models, which get 4WD standard. The Duramax diesel engine is offered across the board, with prices starting just under $39,000, including a $1,595 destination charge. Our test truck, a 2020 GMC Sierra 2500HD AT4 Crew Cab long bed, was $69,385.

Photo by GMC

Huge Torque, Smooth Engine

With 445 horsepower and 910 lb-ft of torque, the GMC Sierra 2500’s Duramax isn’t the most powerful turbodiesel engine offered in this class, but it isn’t far behind its rivals. The strongest version of Ram’s Cummins turbodiesel makes 45 more horsepower than the GMC, though it delivers 90 lb-ft less torque. With 475 hp and 1,050 lb-ft of torque, Ford’s new 2020 Power Stroke diesel is the king of the class. Again, the Chevrolet Silverado Heavy Duty uses the same Duramax engine as the GMC, so it offers the same power.

The engine, which has been around since 2017, is incredibly powerful right off the line. Its torque peaks at just 1,600 rpm, giving you a ton of twist as soon as you touch the throttle. And the new 10-speed automatic, which is smooth and responsive, is geared perfectly to take advantage of the V8’s unique low-speed power. Although the truck weighs a massive 8,300 lbs, it can reach 60 mph in about 6.5 seconds.

Photo by GMC

Incredible Refinement

It wasn’t that long ago that diesel-powered trucks of this size were raw work implements with loud engines and rough rides. That’s just not the case anymore. The 2020 GMC Sierra 2500HD is remarkably refined considering its size and capability.

Like the V6 turbodiesel now offered in the Sierra 1500, this Duramax V8 is smooth, refined, and shockingly quiet. It isn’t quite as hushed as the gas V8, but it doesn’t sound like a Kenworth either. You won’t have to shout over its idle at the drive-thru, and its interior is incredibly quiet on the highway, with very little engine or wind noise.

Photo by GMC

Comfortable Ride and Big Capability

During its redesign, GM’s engineers have fitted the 2020 GMC Sierra Heavy Duty with a new stronger frame, which has increased its towing and hauling ability. The most capable models can now handle a gross combined weight rating of up to 43,500 lbs and tow a 35,500 lb-trailer. The 2500-series trucks have also gotten larger rear axles and a beefier gear set for additional durability.

The wheelbase of our crew cab test vehicle is also 5 inches longer than before. This has increased its rear seat space, which is now cavernous, and smoothed out its ride a bit. GM’s Heavy Duty trucks have featured an independent front suspension for quite some time, but the new model retains the torsion bar design. Although the ride is comfortable, it can be bouncy, and it’s not as smooth as the ride in an equivalent Ford or Ram model. Still, its 3000-lb payload capacity is impressive, and the Sierra handles well, with light steering and an agility that defies its size and weight.

Photo by GMC

Comprehensive AT4 Off-Road Package

Off-road ready packages have become popular in this class. Although the Ram Power Wagon and Ford Tremor still own off-road capability in the Heavy Duty pickup class, the Sierra 2500HD AT4 is far more able off the pavement than other Sierra models.

The four-wheel drive AT4 features special Rancho shocks, optional 20-inch wheels, and 34-inch tall Goodyear Wrangler Trailrunner AT (18-inch tires are standard). A two-speed transfer case with low range is also part of the package along with a locking rear differential, skid plates, hill-descent control to manage the truck’s speed down steep grades, a Traction Select System, which tunes the traction control system for different surfaces, and recovery hooks in its bumper. We were also impressed with its surround camera system, which provides 15 unique camera views and helps you fit this beast in tight spots.

Photo by GMC

Easy to Drive Off Road

Although the 2020 GMC Sierra 2500HD AT4's off-road capability is held back by its low hanging front spoiler and optional side assist steps, the truck was fun to play with at our local off-road park. With about 10 inches of ground clearance below its front differential, there’s an inch more than last year. Unfortunately, there’s only 9 inches of clearance in the rear, and its rear differential is easy to drag over large obstacles.

The Sierra had no problem tackling rocky trails and rutted washes, but in 2WD mode, wheel hop is an issue in deep sand. In four-wheel drive low, the torque of the Sierra’s diesel, its automatic locking rear differential, and its knobby Goodyears made steep climbs easily, but its chassis and body structure don’t seem as solid as the Ram’s or the Ford’s over rutting fire roads. There’s more quiver in the GMC’s cab than there is in the others, and its mirrors and steering wheel vibrate.

Photo by GMC

Cool Multifuction Tailgate

When Ford started making the entire body and bed and its F-Series pickups out of aluminum a number of years ago, other truck manufacturers started getting more serious about exotic materials that save weight and add strength. Today the Sierra's hood, doors, and tailgate are aluminum, though the rest of the truck's body is still steel. GMC offers an optional CarbonPro composite bed, which is made of carbon fiber composite, on its half-ton 1500 model, but not its Heavy Duty trucks.

SLT, AT4, and Denali models come standard with GMC’s MultiPro Tailgate, which is a cool and clever design with six functions and positions including a load-stop, a standing workstation, and a step. The Sierra’s bedside steps and cornerstep rear bumper also make bed access easier. GMC has also lowered the truck’s bed lift-in height by an inch compared to the 2019 Sierra Heavy Duty, making it easier to load cargo and hitch a fifth-wheel or gooseneck trailer.

Photo by GMC

Comfortable and Functional Interior

The GMC’s cabin is comfortable, attractively, and functional with a giant center console, huge door bins, two enormous cupholders, two gloveboxes, and extremely comfortable seats. It’s also properly ergonomic with a height-adjustable driver’s seat, a tilt and telescopic steering wheel, and a mix of analog and digital gauges. To the left of the steering wheel are a push-button parking brake and buttons to control the 4WD system, which engages smoothly. Our test truck also featured heated and cooled seats, a heated steering wheel, and Apple CarPlay and Android Auto. A built-in Wi-Fi hotspot is standard on most models and wireless phone charging is available.

Unfortunately, the Sierra’s cabin feels a bit cheap and dated for such an expensive truck, due to its extensive hard plastics and smallish 8-inch touchscreen. The Ram’s interior remains the most luxurious in this class, with impressive detailing and a massive optional touchscreen.

Photo by GMC

A Long List of Advanced Driver Aids

Ford was once leading the safety tech race in this class, but GMC has caught up. Our Sierra AT4 was packed with high-tech driver aids and safety systems.

Optional packages on our test vehicle included a forward collision warning, automatic emergency braking with pedestrian detection, automatic high beams, lane-keeping assist with a lane-departure warning, adaptive cruise control, front and rear parking sensors, a blind-spot monitor with a rear cross-traffic alert, and GMC's Safety Alert Seat, which vibrates the driver's seat in place of alarm chimes. 

Photo by GMC

Final Thoughts

There’s a lot to like about the 2020 GMC Sierra 2500HD. It’s not only more attractive than the Chevrolet Silverado, but it’s one of the better-looking trucks in its class.

It’s also more spacious than many rivals and cruises effortlessly on the highway, and our diesel-powered test truck averaged 18 mpg in mixed driving, which included a half-day of off-road play. What's more, the Sierra offers impressive refinement, high-tech safety features, and awesome capability. If a diesel-powered heavy-duty pickup is what you want, the 2020 GMC Sierra 2500HD is a solid choice.

Photo by GMC