The GMC Sierra 3500HD, specifically the fifth generation (GMTT1XX) Crew Cab Long Bed model produced from 2020 to 2023, represents GMC’s heavy-duty full-size pickup truck offering. This variant, equipped with the 6.6-liter Duramax turbocharged diesel V8 engine producing 445 horsepower and paired with a 10-speed Allison automatic transmission, and a four-wheel drive (4WD) dual rear wheel (DRW) configuration, was positioned as a premium work truck and towing solution within the Sierra 3500HD lineup. It catered to buyers needing substantial payload and towing capacity without sacrificing interior comfort or advanced technology.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD V (GMTT1XX) Crew Cab Long Bed |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) 4WD DRW Automatic |
| Start of production | 2020 |
| End of production | 2023 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.5 kg/Hp, 118.2 Hp/tonne |
| Weight-to-torque ratio | 3.1 kg/Nm, 327.8 Nm/tonne |
| Power | 445 Hp @ 2800 rpm |
| Power per litre | 67.4 Hp/l |
| Torque | 1234 Nm @ 1600 rpm (910.15 lb.-ft. @ 1600 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Duramax L5P |
| Engine displacement | 6604 cm3 (403 cu. in.) |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 103 mm (4.06 in.) |
| Piston Stroke | 99 mm (3.9 in.) |
| Compression ratio | 16:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Diesel Commonrail |
| Engine aspiration | Turbocharger, Intercooler |
| Valvetrain | OHV |
| Engine oil capacity | 9.5 l (10.04 US qt | 8.36 UK qt) |
| Coolant capacity | 29.1 l (30.75 US qt | 25.6 UK qt) |
| Kerb Weight | 3765 kg (8300.4 lbs.) |
| Max. weight | 6350 kg (13999.35 lbs.) |
| Max load | 2585 kg (5698.95 lbs.) |
| Fuel tank capacity | 136 l (35.93 US gal | 29.92 UK gal) |
| Permitted trailer load with brakes (12%) | 9072 kg (20000.34 lbs.) |
| Length | 6759 mm (266.1 in.) |
| Width including mirrors | 2457 mm (96.73 in.) |
| Height | 2033 mm (80.04 in.) |
| Wheelbase | 4369 mm (172.01 in.) |
| Front track | 1731 mm (68.15 in.) |
| Rear (Back) track | 1905 mm (75 in.) |
| Ride height (ground clearance) | 264 mm (10.39 in.) |
| Drivetrain Architecture | All wheel drive (4×4). Internal Combustion engine. The ICE drives the rear wheels permanently, and the front wheels are driven through an electrically or mechanically operated clutch if necessary. |
| Number of gears and type of gearbox | 10 gears, automatic transmission Allison |
| Front suspension | Coil spring, Double wishbone, Transverse stabilizer |
| Rear suspension | Rigid axle suspension, Leaf spring |
| Front brakes | Ventilated discs, 350×40 mm |
| Rear brakes | Ventilated discs, 355×40 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Electric Steering |
| Tires size | 235/80 R17; 265/70 R17; 245/75 R17; 265/70 R18; 265/60 R20 |
| Wheel rims size | 7.5J x 17; 8J x 18; 8.5J x 20 |
INTRODUCTION
The 2020-2023 GMC Sierra 3500HD Crew Cab Long Bed with the 6.6L Duramax diesel and 10-speed Allison automatic represents a significant evolution in GMC’s heavy-duty truck offerings. Built on the GMTT1XX platform, this generation aimed to provide a more refined and capable experience than its predecessors. The DRW configuration, coupled with the powerful Duramax engine, specifically targeted customers requiring maximum towing and hauling capabilities, such as those in the construction, agriculture, and equine industries. This variant sat at the top of the 3500HD range in terms of capability, often equipped with premium trim packages like Denali or AT4.
Powertrain & Engine Architecture
The heart of this Sierra 3500HD is the Duramax L5P 6.6-liter turbocharged diesel V8. This engine utilizes a cast iron block and aluminum cylinder heads, featuring direct injection and a variable geometry turbocharger. The common rail fuel injection system delivers fuel at extremely high pressures, optimizing combustion efficiency and power output. The engine’s OHV valvetrain contributes to its durability and low-end torque characteristics. The 10-speed Allison automatic transmission, a significant upgrade from previous generations, provides closer gear ratios for improved acceleration and towing performance. This transmission is electronically controlled and features a heavy-duty torque converter designed to handle the engine’s substantial output. The transmission’s ten forward gears allow the engine to operate in its optimal power band more frequently, enhancing both fuel economy and responsiveness.
Driving Characteristics
The combination of the 445 horsepower and 910 lb-ft of torque delivered by the Duramax engine, coupled with the 10-speed Allison transmission, results in a truck that feels remarkably composed even when heavily loaded. The DRW configuration provides enhanced stability and weight distribution, particularly when towing. While not a sports truck, the Sierra 3500HD offers surprisingly responsive acceleration for its size and weight. The Allison transmission shifts smoothly and efficiently, minimizing gear hunting and providing ample power for highway passing and uphill climbs. Compared to the 6.6L gasoline engine option, the Duramax diesel provides significantly more torque at lower RPMs, making it ideal for demanding tasks. Compared to earlier Duramax engines, the 10-speed Allison offers improved fuel economy and a more refined driving experience.
Equipment & Trim Levels
The Sierra 3500HD Crew Cab Long Bed with the Duramax engine was typically available in SLE, SLT, AT4, and Denali trim levels. Standard features generally included a touchscreen infotainment system with Apple CarPlay and Android Auto compatibility, a rearview camera, and a suite of safety features. Higher trim levels added features such as leather upholstery, heated and ventilated seats, a premium sound system, and advanced driver-assistance systems like adaptive cruise control and lane departure warning. Optional extras included a power sunroof, a rear-seat entertainment system, and various towing packages. The Denali trim, in particular, offered a luxurious interior with unique styling cues and premium materials.
Chassis & Braking
The Sierra 3500HD features a fully boxed frame designed for strength and rigidity. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs a leaf spring setup. The DRW configuration utilizes two rear axles, increasing the truck’s load-carrying capacity and stability. The braking system consists of ventilated discs at all four wheels, providing ample stopping power even when heavily loaded. An Anti-lock Braking System (ABS) is standard. The steering system is a rack-and-pinion setup with electric power steering, offering precise control and a comfortable driving experience.
Market Reception & Comparison
The 2020-2023 GMC Sierra 3500HD with the Duramax diesel engine received generally positive reviews from automotive critics. It was praised for its powerful engine, smooth transmission, comfortable ride, and impressive towing and hauling capabilities. Fuel economy, while improved over previous generations, remained a concern for some reviewers, typical for a heavy-duty diesel truck. Compared to competitors like the Ford Super Duty and Ram 3500, the Sierra 3500HD was often seen as offering a more refined interior and a more sophisticated driving experience. Reliability ratings have been generally good, although some owners have reported issues with the diesel exhaust fluid (DEF) system.
Legacy
The Duramax L5P engine and 10-speed Allison transmission combination has proven to be a durable and reliable powertrain. These trucks continue to hold their value well in the used car market, particularly those equipped with the DRW configuration and premium trim levels. The GMTT1XX generation Sierra 3500HD represents a high point in GMC’s heavy-duty truck offerings, providing a compelling blend of capability, comfort, and technology. As these trucks age, proper maintenance and adherence to recommended service intervals will be crucial to ensuring their long-term reliability and performance.
