The GMC Sierra 3500HD, specifically the fifth generation (GMTT1XX) 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 system, was positioned as a premium work and towing solution. The Crew Cab Long Bed configuration offered increased passenger space and cargo capacity, making it a popular choice for both commercial and personal use. This model year marked a significant redesign for the Sierra HD line, focusing on enhanced capability, technology, and interior refinement.
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 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 | 8.3 kg/Hp, 120.6 Hp/tonne |
| Weight-to-torque ratio | 3 kg/Nm, 334.4 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 | 3690 kg (8135.06 lbs.) |
| Max. weight | 5557 kg (12251.09 lbs.) |
| Max load | 1867 kg (4116.03 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 | 2079 mm (81.85 in.) |
| Height | 2049 mm (80.67 in.) |
| Wheelbase | 4369 mm (172.01 in.) |
| Front track | 1731 mm (68.15 in.) |
| Rear (Back) track | 1736 mm (68.35 in.) |
| Ride height (ground clearance) | 283 mm (11.14 in.) |
| Drivetrain Architecture | All wheel drive (4×4). Internal Combustion engine. |
| Number of gears and type of gearbox | 10 gears, automatic transmission Allison |
Powertrain & Engine Architecture
The heart of this Sierra 3500HD is the Duramax L5P 6.6-liter V8 diesel engine. This engine utilizes a cast iron block and aluminum cylinder heads, contributing to its durability and weight. The L5P features a variable geometry turbocharger (VGT) and an intercooler to maximize power and efficiency. The engine employs a high-pressure common rail direct fuel injection system, delivering fuel directly into the cylinders at extremely high pressures for optimized combustion. The overhead valve (OHV) configuration, while traditional, is known for its robustness and lower complexity. The 10-speed Allison automatic transmission, introduced with this generation, replaced the previous 6-speed unit. This transmission provides closer gear ratios, improving both acceleration and fuel economy. The Allison is renowned for its durability and ability to handle the high torque output of the Duramax engine.
Driving Characteristics
The combination of the 445 horsepower and 910 lb-ft of torque delivered by the Duramax engine and the 10-speed Allison transmission results in impressive towing and hauling capabilities. The 10-speed transmission keeps the engine in its optimal power band, even when carrying heavy loads or climbing steep grades. Compared to the 6.6L gasoline engine option, the Duramax provides significantly more low-end torque, making it ideal for demanding tasks. While not a sports truck, the Sierra 3500HD offers a surprisingly comfortable ride, especially with the Crew Cab configuration. The four-wheel drive system provides enhanced traction in various conditions, making it suitable for both on- and off-road use. The automatic transmission, while smooth, doesn’t offer the same level of driver engagement as a manual transmission.
Equipment & Trim Levels
The Sierra 3500HD offered a range of trim levels, with this Duramax/Allison combination typically found in the SLT, AT4, and Denali trims. Standard features included a user-friendly infotainment system with Apple CarPlay and Android Auto compatibility, a rearview camera, and a suite of safety features. Higher trims added features like leather upholstery, heated and ventilated seats, a premium sound system, and advanced driver-assistance systems such as adaptive cruise control and lane departure warning. The Crew Cab configuration provided ample space for passengers, while the long bed offered a generous cargo area. Optional extras included a power sunroof, a rear-seat entertainment system, and various towing packages.
Chassis & Braking
The Sierra 3500HD utilizes a fully boxed frame for enhanced rigidity and durability. The front suspension consists of coil springs and a double wishbone setup, while the rear suspension employs leaf springs. This configuration is designed to handle heavy loads and provide a stable ride. The braking system features ventilated discs at all four wheels, providing ample stopping power. Anti-lock brakes (ABS) are standard. Due to the truck’s weight, the rear brakes are slightly larger (360x34mm) than the front brakes (350x40mm). Electric power steering provides a responsive and comfortable steering experience.
Market Reception & Comparison
The 2020-2023 GMC Sierra 3500HD with the Duramax diesel engine and 10-speed Allison transmission was generally well-received by critics and consumers. It was praised for its powerful engine, smooth transmission, and comfortable ride. Compared to the Ford Super Duty and Ram 3500, the Sierra 3500HD offered a competitive combination of capability, technology, and refinement. Fuel economy, while improved with the 10-speed transmission, remained relatively low compared to lighter-duty trucks. Reliability has been generally good, although some owners have reported issues with the diesel emissions system.
Legacy
The GMTT1XX generation Sierra 3500HD, particularly the Duramax/Allison combination, has established itself as a capable and reliable heavy-duty truck. On the used car market, these trucks hold their value well due to their proven durability and towing capacity. The L5P Duramax engine is known for its longevity, and with proper maintenance, can exceed 200,000 miles. The 10-speed Allison transmission has also proven to be a robust and dependable unit. This generation of Sierra 3500HD continues to be a popular choice for those needing a powerful and capable truck for work or recreation.
