2021 GMC Sierra 3500HD

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2021 GMC Sierra 3500HD Review: The Big Kahuna

by Aiden Eksteen

In the vanguard of heavy-duty pickup truck titans, the 2021 GMC Sierra 3500HD may not be the paragon amongst its vehement rivals but with its authoritarian presence, potent powertrains, and near-unassailable dependability, it's the big kahuna of GMC's Sierra line and a very worthy vehicle in the classification. Rumbling beneath the Sierra 3500HD's hulking hood is a 6.6-liter V8 engine that musters 401 horsepower and 464 lb-ft of torque. However, GMC offers an even mightier Duramax turbodiesel V8 as an option for those who are really serious about hauling. The automaker has been continuously improving the fourth-generation Sierra 3500HD pickup, with this year's model receiving some nifty trailer-assistance technology and additional safety systems. There are, however, still a few flaws that hurt the Sierra 3500HD's chances against the likes of the RAM 3500, Ford F-350 Super Duty, and the Chevrolet Silverado 3500HD.

Read in this review:

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2021 GMC Sierra 3500HD Changes: What’s The Difference vs The 2020 Sierra 3500HD?

The GMC Sierra was completely redesigned for 2020 to bring it up to date in its class. As such, not much changes for 2021, except for some detail specification, trim, spec, and color changes. New trailer-assistance safety features have become available, such as a trailer-length indicator and jack-knife alert, and towing capacity is up. The MultiPro tailgate has now also been added as standard equipment to the SLE trim. The Denali trim gets a bed-view camera and an HD 360-degree camera and is available in a special Diamond Edition with power-retractable running boards and black 20-inch alloys. A high-clearance step and mud tires have been added to the off-road AT4 trim's options. Lastly, three new paint colors are added for 2021.

Pros and Cons

  • Optional V8 diesel engine is potent
  • Refined 10-speed automatic gearbox
  • Great maximum towing capacity
  • Advanced trailer-assistance features
  • Exceptional reliability expectations
  • Brakes could provide more stopping power
  • Authoritarian exterior design is polarizing
  • Cabin design and quality is disappointing
  • Low overall safety rating

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2021 GMC Sierra 3500HD Trims and Prices

See trim levels and configurations:

Trim Engine Transmission Drivetrain Price (MSRP)
6.6L V8 Gas
6-Speed Automatic
Rear-Wheel Drive
Four-Wheel Drive
6.6L V8 Gas
6-Speed Automatic
Rear-Wheel Drive
Four-Wheel Drive
6.6L V8 Gas
6-Speed Automatic
Rear-Wheel Drive
Four-Wheel Drive
6.6L V8 Gas
6-Speed Automatic
Four-Wheel Drive
6.6L V8 Gas
6-Speed Automatic
Four-Wheel Drive

Sierra 3500HD Exterior

2021 GMC Sierra 3500HD Front View Driving GMC
2021 GMC Sierra 3500HD Side View Driving GMC
2021 GMC Sierra 3500HD Side Perspective Driving GMC
See All 2021 GMC Sierra 3500HD Exterior Photos


  • Length 235.5 in
  • Wheelbase 141.6 in
  • Height 80.9 in
  • Max Width 81.8 in

Exterior Colors

Sierra 3500HD Performance

2021 GMC Sierra 3500HD Side Angle Driving GMC
2021 GMC Sierra 3500HD Forward View GMC
2021 GMC Sierra 3500HD Wheel GMC

Engine and Transmission

The source of the 2021 Sierra 3500HD's prodigious power is a 6.6-liter V8 gasoline engine that's been modulated for 401 hp and 464 lb-ft. A 6-speed automatic transmission is appointed to manage outputs and does so to either a rear-wheel drive or all-wheel drivetrain depending on the config chosen. GMC offers the Sierra 3500HD with a 6.6-liter Duramax turbodiesel 8-cylinder unit that generates massive outputs of up to 445 hp and 910 lb-ft for those serious about towing. It comes paired with a polished 10-speed automatic transmission. General performance, payload, and towing capacities depend on the powertrain and body configurations chosen, but the Regular 4-door Cab Heavy-Duty Diesel with the RWD setup and gooseneck hitch will tow a maximum of 36,000 lbs.

  • Engines
    6.6L Turbo V8 Diesel, 6.6L V8 Gas
  • Transmissions
    10-Speed Automatic, 6-Speed Automatic
  • Drivetrains
    4X4, RWD

Sierra 3500HD Gas Mileage

  • Fuel Tank Capacity
    36.0 Gallons
* 2021 GMC Sierra 3500HD 2WD Regular Cab 142"

Sierra 3500HD Interior

2021 GMC Sierra 3500HD Dashboard GMC
2021 GMC Sierra 3500HD Central Console GMC
2021 GMC Sierra 3500HD Steering Wheel Design GMC
See All 2021 GMC Sierra 3500HD Interior Photos

Seating and Interior Space

  • Seating capacity
  • Front Leg Room 44.5 in
  • Front Head Room 43.1 in

Sierra 3500HD Trunk and Cargo Space

2021 GMC Sierra 3500HD Center Armrest Bin GMC
2021 GMC Sierra 3500HD Trunk Space GMC
2021 GMC Sierra 3500HD Top View GMC

Sierra 3500HD Safety and Reliability


  • Warranty Note:
    Preliminary 2021 Warranty \ 
  • Basic:
    3 Years \ 36,000 Miles
  • Drivetrain:
    5 Years \ 60,000 Miles
  • Drivetrain Note:
    HD Duramax Diesel: 5 Years \ 100,000 Miles; Qualified Fleet Purchases: 5 Years
  • Rust-Through:
    6 Years \ 100,000 Miles
  • Corrosion:
    3 Years \ 36,000 Miles
  • Roadside Assistance:
    5 Years \ 60,000 Miles
  • Roadside Assistance Note:
    HD Duramax Diesel: 5 Years \ 100,000 Miles; Qualified Fleet Purchases: 5 Years
  • Maintenance Note:
    1 Year \ 1 Visit

US NHTSA Crash Test Result

NHTSA safety ratings are not available at this time.

Verdict: Is the 2021 GMC Sierra 3500HD A Good Truck?

The 2021 GMC Sierra 3500HD is most certainly a highly proficient and exceedingly dependable workhorse, but it does have quite a few drawbacks that hinder its standing alongside the competition. Its authoritarian aesthetic may be polarizing for some, but its sharp and bulky lines and its over-the-top ruggedness in a selling point for many. Unfortunately, no matter your taste, the Sierra's interior just feels cheap when compared to the interiors of its main competitors, particularly the Silverado's. The premium, heavy-duty pickup truck segment is an extremely competitive one, and automakers are going above and beyond to cram their offerings full of value. But GMC has fallen short on the cabin-quality side of things and, worse, the NHTSA and the IIHS's safety review of the 2021 GMC Sierra 3500HD proved substandard.

Nevertheless, both its V8-equipped powertrains are phenomenal and accord the Sierra 3500HD with some seriously substantial payload and towing capabilities. As with all pickups in this class, however, it chugs fuel like an avid gamer chugs energy drinks. It's also been rated as one of the most dependable heavy-duty trucks money can buy, so you know it will stand the test of time and never let you down.

What GMC Sierra 3500HD Model Should I Buy?

With so many powertrain, cab, and cargo bed configurations, let alone trims, available for the Sierra 3500HD truck, the decision you make will inevitably come down to what you'll need it for. The starting price of the 2021 GMC Sierra 3500HD pickup truck comes in at $37,400 for the US market, which is relatively standard for these cars. If you're a simple admirer of pickup trucks in general and want the best-of-the-best from the GMC Sierra line, then the top-spec Denali is the way to go along with the Duramax turbodiesel engine, 4WD setup with the dual-rear wheels, and extended cargo bed.

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