2021 GMC Sierra AT4 Diesel

This should be at the top of the list for anyone looking at a half-ton truck.
This should be at the top of the list for anyone looking at a half-ton truck.

by Zack Zeraldo | January 29, 2021


Pickup owners tend to pile on mileage, so despite the massive progress trucks have made with fuel consumption, more economy is always a good thing. Diesel engines have been picking up interest in the light-duty segment, as the fuel of choice for three-quarter ton and larger trucks for decades now, but only now are these smaller engines refined enough for duty in the more popular half-ton trucks. So what better time than now to check out GM’s Duramax 3.0-liter inline-six, in the also new 2021 GMC Sierra AT4 Diesel.

The Sierra was fully redesigned for 2019, so for 2020 comes the new AT4 package which adds a factory 2-inch lift with beefy proper all-terrain tries, blacked out trim, LED headlamps, and big red tow hooks in the front, just in case. It’s a mean looking truck, and while I personally haven’t quite settled on the Sierra’s latest body style, the lift kit, big tires and black-out package do make this particular truck a lot more pleasing to the eye.

The AT4 is more than just a lift kit and some appearance goodies though; selecting this trim adds some real off-road credentials with an Autotrac two-speed transfer case, Rancho monotube shocks, additional skid plates and the Traction Select program with off-road mode. Additionally, AT4’s come with GM’s tow package, including the ProGrade trailering guidance system and in-vehicle trailer monitoring. The package isn’t stingy on creature comforts either, including gorgeous heated and ventilated leather seats with Kalahari accents.

I’ve been a fan of GM’s truck interiors for many years and 2020 is no exception. It’s extremely roomy and airy, moreso than the previous generation, with loads of space for passengers to sprawl out in this configuration. Here, function rules and you get one of the cleanest and most informative clusters in the business, a fantastic center console with massive cup-holders, a huge rubber tray and an under arm-rest storage bin the size of a small cooler.

The fancy leather seats add a lot more elegance to the space than one might expect; but while all the latest and greatest tech and features are here, this is not the fully decked out cowboy Cadillac (the Sierra Denali fills that void), so expect to find some chintzy plastics here and there – it’s a pickup after all, and plastics make for easy cleanup.

As far as technology goes, it’s all here including an eight-inch infotainment screen with Apple CarPlay and Android Auto capability. You also get dual-zone automatic climate control with rear vents, and enough USB charge ports and 120V outlets to run a small office. Everything is laid out very logically inside and includes real knobs and buttons for the most common functions such as volume, tuner, and heated seat and steering wheel controls.

The Sierra AT4 comes standard with GM’s tried and true 5.3-liter V8, or for a small fee ($2,895) you can step up to the punchy 6.2-liter powerhouse. However, for a little more ($3,245) you can get into the new 3.0L inline-six diesel. The diesel’s 277 horsepower rating might not sound like much, especially compared to the 420 horsepower claimed by the 6.2-liter V8, but it is the highest horsepower available in a light duty diesel today; and what really matters is how the truck puts it down.

The diesel delivers a big 460 lb-ft. of torque at 1,500RPM. Compare that to the 6.2-liter which also makes 460l lb-ft. but needs 4,100RPM to get there, and you can see why the diesel certainly doesn’t feel like it’s lacking in any way. This translates to power that comes on quick and pulls like a freight train. We drove the truck everywhere; highway, city, rural roads, snowstorms, loaded, unloaded, and never did it need more power.

The only thing I did miss about not having a V8 under the hood of this truck is the sound; GM V8s always sound great on acceleration, and the diesel is typically so well refined that it’s easy to forget you’re not driving a regular V8 powered truck until you step on the gas and that V8 song is replaced by a faint diesel clatter in the cabin. The good news is that the standard 10-speed automatic, one of the best in the business, does an excellent job keeping the Sierra in the perfect gear. Under normal driving conditions it’s not often that the diesel makes itself known.

What almost anyone will appreciate here is the fuel economy. After a busy week, with a good mix of highway and city driving, plus the first snow storm of the season, we observed an average of 11.3L/100km. This is significantly better than the 14.0/100km in a 6.2-powered Sierra last year, and brings the fuel consumption of this truck down to within range of the average large crossover! There are even more savings to be had here with the rated 10.5L/100km city and 9.1L/100km highway.

Another area where this truck really shines is in ride comfort. Even with the all-terrain tires, which are naturally going to be louder than a more highway oriented truck tire, and the two-inch lift kit, the Sierra AT4 handles confidently, with very low levels of noise in the cabin, and exceptional ride quality. The only way to get a better ride in a half-ton truck is with Ram 1500’s air ride system, and the difference is hardly worth the added cost and complexity of the setup.

One last little trick this truck has for us is the CarbonPro carbon fibre bed. This is a true industry first, a truck bed made of carbon fiber. It’s scratch, dent and rust proof, and includes features like task lighting, a 120V outlet, 12 tiedown locations, and convenient tire indents to help make loading vehicles like motorcycle or ATVs easier. The Sierra also boasts the best short-bed cargo bed volume in its class thanks to minimal wheel well intrusion and deep bedsides. Combine this with GM’s six-function MultiPro™ Tailgate and you’ve got a bed that’s ideal for just about any situation or job.

When it comes to pricing, pickup trucks remain one of the few segments out there where you can select loads of a-la-carte options. Combine that with the fact that manufactures tend to offer big discounts at certain times of the year, and pricing variances can be quite wide. The base Sierra AT4 is $60,989; our tester adds the diesel, and a number of options such as; CarbonPro Edition ($4,790) which adds the carbon fiber bed and a slew of nice options such as navigation, wireless charging, rear sliding window and defroster, GoodYear Wrangler Duratrac brand tires, side steps, park assist, lane change, blind spot and rear cross traffic alerts, and the Bose premium sound system.

Our test vehicle also got the Technology Package ($2,520) which adds GM’s fancy rear camera mirror, a bed view camera, heads-up display and a large eight-inch digital driver info center in the gauge cluster. Add to those packages a few stand-alone options and our sticker price came to $74,913. However, current discounting here in Ontario at the time of this writing brings that price back down to a much more reasonable $68,136.

We know the 2020 GMC Sierra AT4 Diesel is a serious contender in its class. Now with a Duramax logo on the side and a new six-cylinder diesel pumping away under the hood, it should be at the top of the list for anyone looking at a half-ton truck – or anyone who packs on enough mileage to make the fuel savings from the diesel worthwhile. There’s really very little compromise here, for some big gains with this powertrain.

See Also:

2020 Ram 1500 Rebel EcoDiesel

2020 Chevrolet Silverado High Country

2019 GMC Sierra Denali

Vehicle Specs
Engine Size
Horsepower (at RPM)
Torque (lb-ft.)
Fuel Efficiency (L/100km, City/Highway/Combined)
Observed Fuel Efficiency (L/100km)
Cargo Capacity (in L)
Base Price (CAD)
As-Tested Price (CAD)
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About Zack Zeraldo

Staff Writer

Despite his relatively young age, Zack has owned more cars than most people will own in their lifetimes. From F-Bodies to pickups and Corvettes, he is a GM enthusiast through and through. When not writing about cars, Zack can be found in his garage messing with one of his eight vehicles.

Current Toys: ’11 XKR, ’85 Trans Am, ’07 DTS Luxury, ’84 Camaro, ’01 Sonoma, ’06 Escalade, ’96 Firebird, ’78 MGB