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First Drive: 2020 GMC Sierra 1500 AT4 Duramax

Posted in News: Features on September 19, 2019
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Contributors: Courtesy of GMC

GMC has had a busy year, between the 2019 Sierra 1500's arrival in showrooms late last year and the debut of the 2020 Sierra HD this summer. Yet in the midst of all those massively important launches, the truck you see here is the one we've been looking forward to driving the most: the 2020 GMC Sierra 1500 Duramax, as equipped in the AT4 off-road special.

Naturally positioned above the GMC Canyon's 2.8L Duramax I-4 and the Sierra HD's 6.6L Duramax V-8, the 3.0L Duramax I-6 features loads of technological advancements, including Active Thermal Management that redirects and prioritizes cooling to keep the diesel engine operating in a uniform, optimal temperature range. A variable intake manifold can prioritize efficiency or output, depending on demand. Also included are a lag-reducing variable-geometry turbocharger and both a high- and low-pressure exhaust gas recirculation system to reduce parasitic boost losses and improve turbo efficiency without increasing emissions.

And underneath all that technical ballyhoo, the three-oh Duramax boasts all the low-tech goodness of an I-6 engine. Its inherent primary and secondary balance precludes the added weight and friction of a balance shaft, and a single set of dual-overhead camshafts further reduces parasitic losses. Finally, an I-6 is just naturally good at providing a wide, flat torque curve, which in this case is 460 lb-ft from 1,500 to 3,000 rpm, if you're wondering, with 95 percent of that peak available from 1,250 rpm.

Slipping behind the wheel, we learn that the marriage of conventional wisdom and new technology is a very happy one indeed. We enjoyed a too-brief taste of the oil-burning mill on an off-road course in the AT4 and came away impressed, not just with the Duramax engine but also with some of the updates GMC has made to the off-roader for 2020.

Over scrabble, large rocks, and logs, we were able to park our feet at about 15 percent throttle and allow the engine's linear torque to pull us through. Climbing hills was a nonissue. And a brief spin through wide-open two-track showed that the diesel could spin up quickly and remain on boil (not as good as the 6.2L V-8, mind, but that's the difference between gas and diesel engines).

What's more, GMC has evidently listened to one of our most significant complaints about the AT4. When we drove it last year, we noticed an unseemly lack of damping in faster sections of off-road. Wheels would drop into divots, the rear end would pogo around and compromise control, and overall suspension and steering response seemed a bit untidy.

However, before heading out in the 2020 AT4 for a taste of the new engine, one GMC representative told us, with a wink, that we might like some of the minor changes the company made to the suspension. Although he wouldn't elaborate further, he was right. Though still making use of the same Rancho shocks and 2-inch-lifted springs as before, the retuned suspension is noticeably more pleasant in exuberant driving. Untoward body motions are better-damped than before, making the 2020 AT4 easier to drive at speed.

With off-road antics in the rear view, we also hitched a Sierra 1500 Denali Duramax to a 7,000-pound trailer and hit the pavement. An exhaust brake keeps everything under control on descents, while a nice groundswell of torque means maintaining freeway speed is a cinch. There's no perceptible steering wheel shake when resting at idle (unlike the slightly grumbly 3.0L Power Stroke V-6 found in the Ford F-150), and the engine runs commendably quietly.

Of course, the 3.0L Duramax's primary shortcoming is its relatively low towing capacity: GMC hasn't released its own official numbers yet, but the Chevrolet Silverado 1500 diesel can only tow 9,300 pounds, quite a bit below the 3.0L Power Stroke's 11,500 pounds and the 3.0L EcoDiesel's 12,560 pounds. The Duramax does offer excellent, class-competitive fuel economy: 23 city/30 highway/25 combined for two-wheel-drive trucks, and 22/26/23 for four-wheelers (including AT4 models).

Obviously, each individual truck buyer's needs vary, but we can say this: The 3.0L Duramax I-6 is an impressively smooth and grunty powerplant, and we commend GM for putting it in the 2020 GMC Sierra 1500. In fact, we'd love to pit the Sierra AT4 Duramax against a Ram Rebel EcoDiesel and see which fullsize pickup would make the better overlander. Given how torquey and smooth the GMC is, it might be a pretty close fight.

2020 GMC Sierra 1500 AT4 Duramax
Vehicle type: Fullsize five-passenger pickup
Base price: N/A
Price as tested: N/A
Engine: 3.0L 24-valve single-turbo diesel I-6, dual overhead cams, direct injection
Transmission: 10-speed automatic
Horsepower: 277 @ 3,750 rpm
Torque: 460 lb-ft @ 1,500-3,000 rpm
Curb weight: N/A
Towing capacity (lb): 9,300 (est)
EPA mileage rating (mpg): 23 city/30 highway/25 combined (2WD); 22/26/23 (4WD)

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