The GMC Sierra 3500HD, in its fifth generation (GMTT1XX), represents GMC’s heavy-duty full-size pickup truck offering. Produced from 2020 to 2023, the Double Cab Long Bed configuration with the 6.6-liter Duramax Turbo Diesel V8 engine producing 445 horsepower and paired with a 10-speed Allison automatic transmission, was a top-tier offering aimed at buyers needing substantial towing and hauling capability. This variant occupied the premium segment of the 3500HD lineup, positioned above the gasoline-powered options and the lower-output diesel trims.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD V (GMTT1XX) Double Cab Long Bed |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) 4WD SRW 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 | 8.1 kg/Hp, 123.2 Hp/tonne |
| Weight-to-torque ratio | 2.9 kg/Nm, 341.6 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 | 29.1 l (30.75 US qt | 25.6 UK qt) |
| Kerb Weight | 3612 kg (7963.1 lbs.) |
| Max. weight | 5511 kg (12149.68 lbs.) |
| Max load | 1899 kg (4186.58 lbs.) |
| Fuel tank capacity | 136 l (35.93 US gal | 29.92 UK gal) |
| Permitted trailer load with brakes (12%) | 6577 kg (14499.8 lbs.) |
| Length | 6514 mm (256.46 in.) |
| Width including mirrors | 2079 mm (81.85 in.) |
| Height | 2054 mm (80.87 in.) |
| Wheelbase | 4127 mm (162.48 in.) |
| Front track | 1731 mm (68.15 in.) |
| Rear (Back) track | 1736 mm (68.35 in.) |
| Ride height (ground clearance) | 284 mm (11.18 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 |
Powertrain & Engine Architecture
The heart of this Sierra 3500HD variant is the Duramax L5P 6.6-liter turbocharged diesel V8. This engine represents a significant evolution of the Duramax design, featuring a cast iron block, aluminum cylinder heads, and a robust rotating assembly. The L5P utilizes a common-rail direct fuel injection system, delivering fuel at extremely high pressures for optimized combustion. The turbocharger, coupled with an intercooler, provides increased air density for enhanced power output. The overhead valve (OHV) valvetrain, while seemingly traditional, is engineered for durability and low-end torque. The 10-speed Allison automatic transmission is a key component, designed to handle the engine’s substantial torque output and provide smooth, efficient shifting. This transmission features electronically controlled shifts and multiple driving modes, including tow/haul mode for optimized performance when towing heavy loads.
Driving Characteristics
The combination of the 445 horsepower Duramax engine and the 10-speed Allison transmission delivers a compelling driving experience. While not a sports truck, the Sierra 3500HD offers ample power for accelerating with a load or maintaining highway speeds. The 10-speed transmission keeps the engine in its optimal power band, providing responsive acceleration. Compared to the 6.6L gasoline engine options, the diesel offers significantly more low-end torque, making it ideal for towing and hauling. Compared to lower-output diesel variants, the 445 hp version provides a noticeable increase in power, particularly when climbing hills or passing other vehicles. The gear ratios in the Allison transmission are well-suited for heavy-duty applications, providing both strong pulling power and reasonable fuel economy.
Equipment & Trim Levels
The Double Cab Long Bed 3500HD with the Duramax engine typically came standard with a well-equipped interior. Features included cloth or leather upholstery (depending on trim level), an 8-inch touchscreen infotainment system with Apple CarPlay and Android Auto compatibility, and a rearview camera. Higher trim levels, such as Denali, added premium features like heated and ventilated front seats, a premium sound system, and advanced safety technologies. Optional extras included a power sunroof, a rear-seat entertainment system, and various towing packages.
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 leaf springs. This configuration provides a comfortable ride while maintaining excellent load-carrying capacity. The braking system consists of ventilated discs at all four wheels, providing ample stopping power even when towing heavy loads. ABS (Anti-lock Braking System) is standard. The rear axle is a solid axle, optimized for durability and towing capacity. Stabilizer bars are included to reduce body roll during cornering.
Market Reception & Comparison
The GMC Sierra 3500HD with the Duramax engine and 10-speed Allison transmission received generally positive reviews from automotive critics. It was praised for its powerful engine, smooth transmission, and comfortable ride. Fuel economy, while not exceptional, was considered reasonable for a heavy-duty truck of its size and capability. 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 smoother ride. Reliability was generally good, although some owners reported issues with the diesel particulate filter (DPF) system.
Legacy
The Duramax L5P engine and 10-speed Allison transmission have proven to be a durable and reliable powertrain combination. In the used car market, these trucks hold their value well, particularly those that have been well-maintained. The L5P Duramax is known for its longevity and ability to withstand high mileage. While the DPF system can require maintenance, the overall reliability of the powertrain is considered excellent. This variant of the Sierra 3500HD remains a popular choice for buyers seeking a capable and reliable heavy-duty truck.
