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The 2020 GMC Sierra HD is available with a 6.6-litre turbodiesel engine.

Doug Firby

Some people will tell you that trailering is fun. Don’t believe them.

If you’re beating down a two-lane road with a 10-metre anchor dragging behind you and a string of cars you can’t even see trying to get by, the experience can ramp up your blood pressure quicker than a tax audit.

GMC affirmed that towing anxiety is a real thing when it laid the groundwork for its 2020 line of heavy-duty trucks. Researchers talked to more about 7,000 people in the United States about the experience of pulling a large trailer, says Tim Herrick, the project’s executive chief engineer.

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“Fifty-seven per cent said that towing was stressful,” Herrick said. “The other 43 per cent lied.”

The mandate was clear for GMC: Make a HD truck that is big, powerful and “tech’d up” enough to turn a summer schlep into the mellow experience it was always meant to be.

The result – the 2020 GMC Sierra HD – ticks all the boxes. The new generation of HD Sierras bumped claimed towing capacity to more than 16,000 kilograms, an increase of 52 per cent over the previous model. It beefed up its engine and transmission options. And on the tech front, the available options include up to 15 camera views all around you – including an “invisible trailer” view that lets you see right behind your trailer.

A step has been integrated into the side of the HD Sierra, making it easier to reach into the cargo box.

Doug Firby

At the core of this remake is the powertrain, which puts the accent on the first word. Its engine options include a hearty 6.6-litre gasoline V-8, which produces 401 horsepower. More significant is GMC’s 6.6-litre turbodiesel mated to a 10-speed Allison automatic transmission designed specifically for heavy loads. The diesel puts out 445 horsepower and, more importantly, 910 lb.-ft. of torque – the true measure of pulling power.

It also added a badly needed dose of sportiness through the introduction of the AT4 off-road appearance and performance package. This model joins the existing higher-end Denali and Elevation trim levels featured at a recent media event in Jackson Hole, Wyo.

The AT4 is a refreshing alternative to the Denali, which nevertheless remains the highest-selling trim level. The AT4 swaps out the Denali’s retina-searing and – sorry loyalists – terribly dated bright chrome in favour of dark chrome exterior finishes and features body-coloured front and rear bumpers and grille-surround. Red vertical-recovery hooks set off the rough-riding theme. It’s the first time a HD GMC has actually looked like it’s ready to rumble off-road.

There is substance behind the looks, too, with rugged Rancho shocks, skid plates and a locking rear differential. Eighteen-inch wheels are clad in Michelin all-terrain tires, with 20-inch wheels available. Other goodies include hill-descent control, hill-start assist and a surround-vision system that includes a camera view over the crest of the hill – trust me, this is a handy feature.

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Rancho shocks, skid plates and a locking rear differential make the AT4 a confident off-road truck.

Doug Firby

Design director Matt Noone says the “anti-chrome” AT4 has off-road looks and capability, but keeps GMC’s core mission in mind for its HD trucks. The company’s research shows that 93 per cent of heavy-duty truck buyers tow, and half of those buyers pull more than 3,600 kilograms.

“What we did is not go so heavily into off-road that we compromised the towing,” Noone said. “This truck is all about towing.”

That’s obvious when you test out the remarkably useful ProGrade trailering system, which is compatible with many late-model large trailers. The system has an in-vehicle trailering app that can test the trailer lights, run diagnostics on the trailer’s electrics, monitor trailer tire pressure and temperature and run through a departure checklist. You even do the lighting test and predeparture checklist on your smartphone using GMC’s app.

And, boy, can it tow. GM claims the diesel can reach 97 km/h in 19.9 seconds while towing an 8,200-kilogram trailer. In two-lane traffic, getting quickly up to highway speed matters. We got a chance to do even more; GMC invited us to tow loads up to 18,000 kilograms on seven-degree inclines. The diesel dug in and confidently did the job. Was it enjoyable? Not really, but it was reassuring to know your truck can handle any mountain adventure.

New to the HD trucks this year is the MultiPro tailgate, a six-configuration tailgate introduced in light-duty trucks last year. It is available on all trim levels.

The big 6.6-litre diesel has plenty of power for pulling heavy trailers.

Doug Firby/The Globe and Mail

These are massive trucks. A tall in-your-face front grill emphasizes the vehicle’s mass. The whole vehicle stands taller and longer than the model it replaces.

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“HD customers really demand that it’s a heavy-duty look for a heavy-duty truck,” said Chris DePolo, lead development engineer for the HD truck. “But it still has to drive and handle really well.”

And it did. The firm suspension made you feel fully in control, yet was calibrated to smooth out jarring bumps. The cabin itself was roomy and eerily low-noise. Large diesel engines are known for a rattling sound and smelly exhaust – this engine did neither.

“Those old days of noisy diesels, they’re all gone,” DePolo said.

And so, it seems, is the stress. Because these heavy-duty trucks have elevated the art of towing big rigs to a new – and more karmic – level.

Deliveries to Canadian dealerships are to start this fall.

Tech specs

  • Price as tested: $92,113 in 4WD and crew cab configuration
  • Engines: 6.6-litre V-8, 6.6-litre V-8 turbodiesel
  • Transmission/drive: 10-speed automatic; 10-speed Allison on turbodiesel, 2WD and AWD
  • Fuel economy (litres/100km): with 5.3-litre V-8 gasoline engine 15.3 city/11.2 highway; with 3.0 diesel 4WD 10.5 city/9.1 highway
  • Alternatives: Ram 2500, Ford F250


Bright red tow hooks accent the AT4's off-road cred.

Doug Firby

For years the most old-school-looking of the Detroit Three trucks, GMC has finally started to tone down the chrome and add a bit more spice – especially in the AT4, which is new to the HD line. The lines are clean, and the vehicle looks huge. The frowny-face front grill sets this truck’s appearance apart from its Chevrolet cousin, the Silverado HD. Spend enough time with it, and you might slowly develop some affection for its look. You know, like you would for a turtle.


The tasteful treatments found in all brands of higher-trim-level HD trucks redefine the experience of driving a big truck. GMC’s dressiest trim, the Denali, features lots of leather accents, open-pore wood and aluminum finishes. Headroom and legroom are claimed to be best in class. The horizontal switch array under the large touch screen is relatively intuitive. Cabin noise is minimal.


In the weird arms race involving the Detroit Three, GMC’s 2500 line falls just short of the king-of-the-moment, FCA’s Ram, which produces 1,000 lb.-ft. of torque and claims it can tow up to 15,900 kilograms in 3500HD dually form. (Duallys are double wheels on the rear of the pickup that can bear more load than single wheel configurations.) The big number seems pointless – the GMC can easily haul any large trailer and do it with silky smoothness, virtually no vibration and remarkably little noise.


One of the available cameras shows the cargo box.

Doug Firby

There are many, many safety and convenience features. One of my favourites is the array of 15 camera views, which both reduces the risk of mishap and relieves driver stress. The optional 38-centimetre head-up display provides vehicle speed (and posted speed limit), navigation information and an inclinometer for the road grade.


GMC emphasizes the AT4's flexibility and cargo capacity.

Doug Firby

The crew-cab configuration has generous room in front and back. The 5-foot, 9-inch cargo box is standard; the 8-foot box offers 2,364 litres of space, which means you can pretty well bring the whole house with you on vacation.

The verdict: 8.5

This great leap forward in the GMC HD line keeps it firmly apace with its two Detroit competitors and ahead by some measures. To some, it will be overkill. Many buyers will find that the well-outfitted light-duty GMC will do all they need. But if you’re planning to haul big loads or carry heavy payloads, this comfortable, quiet and strong truck really does turn down the stress on long-distance towing.

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The writer was a guest of the automaker. Content was not subject to approval.

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