Big jobs require big trucks and the 2020 GMC Sierra HD rises to the challenge with copious features and massive tow ratings. The Sierra 2500HD and 3500HD share mechanicals with the heavy-duty Chevy Silverado, but the GMC has a distinctly different appearance. Like the Chevy, it faces off against equally powerful rivals such as the Ford Super Duty and Ram HD. While the big-bodied Sierra is equally capable and configurable, its deluxe Denali trim level isn’t quite as fancy as the most dashing heavy-duty Ram’s. Still, the GMC satisfies pickup-truck purists with its refined, brawny Duramax diesel V-8 and trusty Allison transmission. Plus, the 2020 Sierra HD offers a plethora of practical and technological features that range from a clever multifunction tailgate to advanced trailering assists.
What’s New for 2020?
The Sierra 2500HD and 3500HD have been completely redesigned for 2020. Together they get a bolder-looking exterior, reimagined interiors, updated powertrains, substantially increased payload and tow ratings, and unique and inventive features. The HD twins also add a new off-road-oriented model—called AT4—that GMC is starting to proliferate throughout its portfolio. We’ve recently driven the Acadia AT4; the all-new 2021 Yukon will get the kit, too.
Pricing and Which One to Buy
- Base: $35,272
- SLE: $39,035
- SLT: $48,956
- AT4: $55,602
- Denali: $61,218
There are a lot of variables when it comes to configuring a pickup truck—unless it’s the one-size-fits-all Honda Ridgeline. Still, the most popular pickups these days offer a crew cab, so we’d start with that and choose the standard bed on the Sierra 2500HD. We’d steer clear of the rugged AT4 and chrome-laden Denali models despite their enhanced appearance. Instead, we’d recommend picking the SLT trim level and adding all-wheel drive and the Duramax diesel V-8. The SLT comes standard with GMC’s versatile MultiPro tailgate, a heated steering wheel, heated front seats, power-adjustable front seats, and remote start. It also unlocks more options than the lesser SLE trim. We’d pick the SLT Convenience package that includes front bucket seats with ventilated cushions, heated rear seats, and a power-sliding rear window. The Driver Alert packages are also worth adding because they make the behemoth easier to live with thanks to assists such as blind-spot monitoring, lane-departure warning, and front and rear parking sensors.
Engine, Transmission, and Performance
The Sierra HD comes standard with a gas-powered 6.6-liter V-8 that generates 401 horsepower and 464 lb-ft of torque. It pairs with a six-speed automatic transmission and rear- or all-wheel drive. The optional Duramax diesel 6.6-liter V-8 cranks out 445 ponies and 910 lb-ft of twist, and it works through an Allison 10-speed automatic. You can also specify either a single- or dual-rear-wheel axle (known as a “dually”). While we’ve only driven the diesel variant, we did sample the gas-burning powertrain on the internally identical Silverado 2500HD and appreciated its dutiful behavior. However, there’s no arguing that the Duramax/Allison combination is a highlight of the heavy-duty Sierra, and it’s a no-brainer for those who regularly tow substantial loads. The engine is surprisingly refined, and the transmission is very responsive. Together they helped the 2500HD Denali we tested achieve impressively quick acceleration times. The gigantic GMC also has an agreeable ride quality for its breed. Though its steering is vague at highway speeds the Sierra nonetheless feels more agile than its heavy-duty competitors. The trail-ready AT4 model is a more-rugged take on the commonly chrome-riddled rig, with an off-road suspension and a locking rear differential to go with its otherwise blacked-out aesthetic.
Towing and Payload Capacity
The strongest Sierra 3500HD can carry 7442 pounds in its cargo bed and pull as much as 35,500 pounds. However, those massive capacities require the diesel engine, regular cab, rear-wheel drive, and dual-rear-wheel axle. The Sierra 2500HD is only offered with a single-rear-wheel axle, and its burliest version is good for 3979 pounds of payload and 18,500 pounds of towing.
Fuel Economy and Real-World MPG
Since the EPA doesn’t test vehicles as heavy as the Sierra HD and its gigantic competitors, we can only judge their real-world mpg on our highway fuel-economy route. We’ve only tested a Sierra 2500HD Denali with the diesel engine, which earned 17 mpg on the highway. For comparison, the diesel-powered Silverado 2500 LTZ crew cab and Ram 2500 Tradesmen regular cab diesels we tested both managed 19 mpg. Those who stick with the GMC’s standard gas-fed V-8 should expect to see even worse fuel economy than the diesel option.
Interior, Comfort, and Cargo
Inside, the Sierra 2500HD and 3500HD have a huge dashboard that hosts user-friendly switchgear. Most models have a split-folding front bench that can be replaced with a pair of bucket seats and a full center console. The Sierra’s interior can also be optioned with a class-exclusive head-up display, a heated steering wheel, heated-and-cooled front seats, and wireless charging. Unfortunately, the cabin’s panel fits and material quality are mediocre at best. While there’s an abundance of soft touch surfaces throughout, and most models benefit from durable plastics, the top-of-the-line Denali falls woefully short of its luxury billing. The fanciest alternatives from Ram overshadow the GMC largely thanks to their significantly more upscale look and feel. Still, the Sierra HD will please pickup-truck buyers who prioritize practicality and versatility. Along with extensive passenger space in the crew cab, the GMC is littered with handy interior cubby storage. Its standard and long cargo boxes have built-in steps on both sides of the bed and the rear bumper has them at each corner. The box can be further customized with LED lighting, movable tie-downs, and a 120-volt outlet. The heavy-duty Sierra’s biggest showpiece is its innovative multi-function tailgate, which has six different positions that include a work surface and bench. It’s a tailgater’s dream come true.
Infotainment and Connectivity
Every Sierra HD has a standard touchscreen infotainment system with Apple CarPlay and Android Auto. While base models have fewer options, they can still be outfitted with a 120-volt outlet and a mobile hotspot. Most trim levels have an 8.0-inch screen and additional charging ports. All systems include a set of rotary knobs and physical buttons that are easily accessible. The larger touchscreen can be upgraded with built-in navigation, a Bose audio system, SiriusXM satellite radio, and a rear-seat entertainment system. GMC also offers a smartphone app that can be used to remotely control trailer functions. Likewise, the truck’s infotainment system allows users to store different trailer profiles to monitor maintenance.
Safety and Driver-Assistance Features
The 2020 Sierra HD hasn’t been crash tested by the National Highway Traffic Safety Administration (NHTSA) or the Insurance Institute for Highway Safety (IIHS). While the truck can be equipped with various driver-assistance technology, none of it comes standard, and heavy-duty rivals offer even more assists. However, the GMC does have a comprehensive camera system that features up to 15 different viewing modes, including a “transparent” mode that allows the user to virtually see through an attached trailer as if it wasn’t there. Key safety features include:
- Available forward-collision warning and automated emergency braking
- Available blind-spot monitor and rear cross-traffic alert
- Available lane-departure warning
Warranty and Maintenance Coverage
- Limited warranty covers three years or 36,000 miles
- Powertrain warranty covers five years or 60,000 miles
- Complimentary maintenance is covered for the first visit