2020 GMC Sierra 1500 Diesel Road Test and Review

Diesel engines are making a serious comeback in light-duty trucks. Although diesel-powered cars have been pushed aside for now as manufacturers concentrate on hybrids and electric vehicles, the availability of full-size diesel-powered pickups like the 2020 GMC Sierra 1500 is rapidly on the rise.

Traditionally, diesel power has been limited to the largest heavy-duty versions of America’s pickups — rigs designed for extreme towing and job-site duty. The more popular half-ton or light-duty trucks from Chevrolet, GMC, Ford, and Ram were once powered exclusively by gasoline-burning engines. But that’s not the case anymore. For 2020, all four manufacturers are offering their half-ton trucks with six-cylinder diesel engines. Our test truck, a diesel-powered 2020 GMC Sierra 1500 4WD Crew AT4, competes with diesel versions of the Ford F-150, Chevrolet Silverado, and Ram 1500. After time behind the wheel, both on the road and off, it’s clear this is one the best half-ton Sierras that GMC has ever offered.

GMC has been building some of America’s most capable and comfortable trucks since 1912, and the 2020 GMC Sierra 1500 is one of the best-selling full-size pickups in the country. Built in Roanoke, Indiana, the half-ton pickup is available in regular cab, double cab, and crew cab body styles, and they're all offered with 4WD. There are also many trim levels to choose from as well as many engines. The new 3.0-liter Duramax diesel, which is a turbocharged inline six-cylinder, is available on most trim levels, including the SLE, SLT, and the top-of-the-line AT4 and Denali.

The base price of our test truck — a 2020 GMC Sierra 4WD AT4 Crew Cab — was $54,995, including a $1,595 destination charge. The standard engine is a 5.3-liter V8. With a long list of options, including the Duramax diesel engine that costs an extra $2,495, our truck’s MSRP swelled to $66,515.

With a rating of just 277 hp, the new Sierra diesel makes less horsepower than all the truck's other available engines, including the base 295-hp 4.3-liter V6 and the 310-hp turbocharged 2.7-liter four-cylinder. Its 460 lb-ft of torque, however, matches the output of the heartiest 6.2-liter V8. And it peaks at just 1,500 rpm, giving you a ton of twist as soon as you touch the throttle; the V8’s torque doesn’t peak until 4,100 rpm. The diesel is also smooth, refined, and quiet. It isn’t quit as hushed as the standard V8, but it doesn’t sound like a Peterbilt either. You won’t have to shout over its idle at the drive-thru.

Around town, the Sierra’s new diesel offers impressive power, and its 10-speed automatic transmission is smooth, responsive, and well-matched to the six-cylinder’s unique power delivery. Although the Duramax redlines at 5,250 rpm, at full throttle the transmission upshifts at 4,000, which emphasizes the engine’s low-rpm grunt. Unfortunately, there are no paddle shifters. Manual gear selection uses an awkward button on the truck’s old-school column shifter.

Although the Ford F-150 Raptor still owns off-road capability in the full-size pickup class, the Sierra AT4 is far more able off-road than other Sierra models. The four-wheel drive AT4 features a 2-inch suspension lift for additional clearance, a two-speed transfer case with a low range, a locking rear differential, skid plates, Rancho shocks, 18-inch wheels with large Goodyear Wrangler DuraTrac tires (20-inch wheels available), hill-descent control, traction control, and recovery hooks. Although held back by its low-hanging front spoiler and optional assist steps, the Sierra was fun to play with at our local off-road park. With about 9 inches of ground clearance below its differentials, the Sierra had no problem on rocky trails and rutted washes.

In its four-wheel drive's low mode, the torque of the Sierra’s diesel, its automatic locking rear differential, and its knobby Goodyears made steep climbs easily, but in 2WD mode, wheel hop is an issue in deep sand. Also, its chassis and body structure don’t seem as solid as the Ram’s or the Ford’s over rutted fire roads. There’s more quiver in the GMC’s cab than there is in the others.

With its long 147.5-inch wheelbase, the big GMC rides well enough to call it comfortable, but it’s still not as plush as the Ram. Unlike the GMC and the other full-size pickups on the market, the Ram 1500, even in off-road Ram Rebel trim, uses a unique coil-spring rear suspension, which gives class-leading ride quality.

Around town, the Sierra feels agile and light on its feet, with light, quick steering and sharp reflexes. This isn’t a clumsy lumbering truck despite the fact that it weighs over 5,500 lbs. It feels at home on the rural dirt roads and twisty two-lanes of central Michigan, and out on the highway it cruises along effortlessly, its cabin void of unwanted diesel clatter.

When Ford started making the entire body and bed and its F-Series pickups out of aluminum a few 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, and our truck was equipped with the optional Carbonpro bed. It’s made of carbon fiber composite, sort of like the body of a Lamborghini Aventador SVJ, and it's expensive at $3,665. But GMC says it offers increased cargo volume; delivers best-in-class dent, scratch, and corrosion resistance; and weighs 60 lbs less than a traditional bed.

We’re more impressed with the GMC’s MultiPro Tailgate. You’ve probably seen the TV commercials that show off its six functions and positions, which include a load-stop, a standing workstation, and a step. Clever stuff. And the Sierra’s corner-step rear bumper is another example that not all engineering is gratuitous. Sometimes it just makes perfect practical sense and makes bed access much easier. Our Sierra also came standard with LED bed lighting, 12 fixed cargo tie-downs, a bed-mounted 120V power outlet, and a power-sliding rear window.

Of all the Sierra’s available engines, the new Duramax diesel is by far the most fuel-efficient. In 2WD models, the diesel Sierra is rated at 23 mpg city and 30 mpg on the highway. With 4WD, those numbers dip to 22 mpg city and 26 mpg highway, but we were impressed with the smooth operation of the truck’s stop/start feature, which shuts off its engine at idle to save fuel.

The RAM 1500 EcoDiesel V6 gets worse mileage than the Sierra. Its Limited model is rated at 20 mpg city and 29 mpg highway, while the Rebel is rated at 19 mpg city and 29 mpg highway. With its optional Power Stroke turbodiesel 3.0-liter V6, the Ford F-150 is rated at 22 mpg city and 30 mpg highway with 2WD and 20 mpg city and 25 mpg highway for 4x4 models. Lastly, the Chevrolet Silverado is essentially the same truck mechanically as the Sierra, and it’s available with the exact same Duramax diesel and 10-speed transmission, so it gets the same fuel economy as the GMC.

The Sierra's cabin is comfortable, attractively basic, 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 tilting and telescopic steering wheel, and a mix of analog and digital gauges. To the left of the steering wheel is a push-button parking brake and buttons to control the truck's 4WD system. Our test truck also featured heated and cooled seats, a heated steering wheel, and cavernous rear-seat accommodations.

Unfortunately, the GMC's interior feels a bit cheap and dated for a $66,000 truck. Unless you like a lot of hard black plastic and a small 8-inch touchscreen, you’re going to be disappointed. The Ram’s interior is the leader of this field.

Our Sierra AT4 was also packed with high-tech driver aids and safety systems. Its optional Technology Package includes a forward-collision alert, automatic emergency braking with pedestrian detection, adaptive cruise control, a following-distance indicator, automatic high beams, a lane-departure warning with lane-keep assist, and GMC's Safety Alert Seat, which vibrates the driver's seat in place of warning beeps and chimes.

In addition to the carbon composite bed, our truck’s AT4 CarbonPro Edition Package also added front and rear parking sensors, blind-spot monitoring with a rear cross-traffic alert, a Bose premium audio system, wireless smartphone charging, and a laundry list of other infotainment upgrades.

As we said, diesel engines are making a serious comeback in light-duty trucks, but truck buyers should keep in mind that diesel isn’t always the answer. Yes, a truck with a diesel engine will get better mileage, but its diesel engine costs thousands more and diesel fuel is rarely cheaper than 87-octane gasoline. In fact, as of this writing, the national average price of diesel fuel is about $1 more per gallon than regular gasoline. Plus, all-new diesel pickups require frequent refilling of their diesel exhaust fluid tanks, which help them meet emissions requirements.

That said if it’s a diesel-powered half-ton full-size pickup you want, then the 2020 GMC Sierra is a solid choice. It offers more horsepower than its rivals, and only the Ram EcoDiesel makes more torque. It’s also very comfortable, and the AT4 offers above-average off-road capability for this class.