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 model year covered here focuses specifically on the Regular Cab, Long Bed configuration equipped with the 6.6-liter Duramax Turbo 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) drivetrain. This variant occupied a premium position within the Sierra 3500HD lineup, targeting buyers requiring substantial towing and hauling capabilities without sacrificing refinement. It served as a workhorse for commercial applications and a robust choice for individuals needing serious truck power.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD V (GMTT1XX) Regular 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 | 2 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 7.9 kg/Hp, 126.3 Hp/tonne |
| Weight-to-torque ratio | 2.9 kg/Nm, 350.3 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 | 3523 kg (7766.89 lbs.) |
| Max. weight | 6350 kg (13999.35 lbs.) |
| Max load | 2827 kg (6232.47 lbs.) |
| Fuel tank capacity | 106 l (28 US gal | 23.32 UK gal) |
| Permitted trailer load with brakes (12%) | 9072 kg (20000.34 lbs.) |
| Length | 5982 mm (235.51 in.) |
| Width including mirrors | 2457 mm (96.73 in.) |
| Height | 2038 mm (80.24 in.) |
| Wheelbase | 3595 mm (141.54 in.) |
| Front track | 1731 mm (68.15 in.) |
| Rear (Back) track | 1905 mm (75 in.) |
| Ride height (ground clearance) | 266 mm (10.47 in.) |
| Drivetrain Architecture | All wheel drive (4×4). ICE drives rear wheels, front wheels engaged via clutch. |
| 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 Regular Cab Long Bed with the 6.6L Duramax diesel and Allison automatic transmission represents a significant offering in the heavy-duty truck segment. Built on the GMTT1XX platform, this configuration was designed for demanding tasks, prioritizing towing capacity and payload. The Regular Cab layout, combined with the long bed, catered to customers who needed maximum cargo space and a straightforward, work-oriented truck. This particular trim level aimed to bridge the gap between basic work trucks and more luxurious HD models, offering a balance of capability and comfort.
Powertrain & Engine Architecture
At the heart of this Sierra 3500HD lies the Duramax L5P 6.6-liter turbocharged diesel V8 engine. This engine is a cornerstone of GMC’s heavy-duty lineup, known for its robust construction and impressive torque output. The L5P utilizes a cast iron block, aluminum cylinder heads, and a variable geometry turbocharger with an intercooler to deliver 445 horsepower at 2800 rpm and a massive 910 lb-ft of torque at 1600 rpm. The engine employs a high-pressure common rail direct fuel injection system, contributing to its efficiency and power delivery. The overhead valve (OHV) valvetrain, while a more traditional design, is known for its durability and simplicity. The engine requires 9.5 liters (10.04 US quarts) of oil and 29.1 liters (30.75 US quarts) of coolant. A diesel particulate filter is included to meet emissions standards.
The engine is mated to a 10-speed Allison automatic transmission, a crucial component in maximizing the truck’s towing and hauling capabilities. This transmission provides a wide gear ratio spread, allowing the engine to operate in its optimal power band more frequently. The Allison transmission is renowned for its durability and smooth shifting characteristics, even under heavy loads.
Driving Characteristics
The combination of the Duramax engine and the 10-speed Allison transmission results in a driving experience focused on effortless power and control. The 910 lb-ft of torque is readily available, making towing and hauling heavy loads feel remarkably manageable. While not designed for outright speed, the truck offers ample acceleration for everyday driving and highway merging. The 10-speed transmission keeps the engine in its sweet spot, minimizing the need for frequent downshifts. Compared to the gasoline-powered Sierra 3500HD variants, the diesel offers significantly more low-end torque, making it ideal for demanding tasks. Compared to higher output versions of the Duramax, this configuration prioritizes a balance of power and efficiency, rather than outright maximum performance.
Equipment & Trim Levels
The Sierra 3500HD Regular Cab Long Bed with the Duramax engine typically came standard with features like air conditioning, power windows and locks, a basic infotainment system with a touchscreen display, and a rearview camera. Interior upholstery was typically vinyl or cloth, reflecting the truck’s work-oriented nature. Optional extras included features like heated seats, a premium audio system, navigation, and various driver-assistance technologies. The trim level often included chrome exterior accents and upgraded interior materials compared to base models.
Chassis & Braking
The Sierra 3500HD features a robust chassis designed to handle heavy loads. The front suspension utilizes coil springs and a double wishbone setup with a transverse stabilizer bar, while the rear suspension employs a traditional leaf spring configuration. This setup provides a comfortable ride while maintaining excellent load-carrying capacity. Braking duties are handled by ventilated disc brakes on all four wheels, measuring 350x40mm at the front and 355x40mm at the rear. An Anti-lock Braking System (ABS) is standard. The truck features a rack and pinion steering system with electric power steering for improved maneuverability.
Market Reception & Comparison
The GMC Sierra 3500HD with the Duramax diesel engine consistently received positive reviews for its towing and hauling capabilities. Critics praised the engine’s power and torque, as well as the smooth operation of the Allison transmission. Fuel economy, while not a primary concern for heavy-duty truck buyers, was considered competitive within the segment. Compared to the gasoline-powered Sierra 3500HD models, the diesel offered superior fuel efficiency when towing heavy loads. Compared to other heavy-duty trucks like the Ford Super Duty and Ram 3500, the Sierra 3500HD was often seen as a well-rounded option, offering a good balance of capability, comfort, and refinement.
Legacy
The Duramax L5P engine and Allison 10-speed transmission combination has proven to be a reliable and durable powertrain. These trucks have maintained strong resale values in the used car market, reflecting their reputation for dependability. Properly maintained, these engines can easily exceed 200,000 miles. The GMTT1XX Sierra 3500HD continues to be a popular choice for buyers seeking a capable and long-lasting heavy-duty truck, and remains a workhorse for many years to come.
