The GMC Sierra 3500HD IV (GMTK2XX) Double Cab Long Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 445 horsepower, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2017 to 2019, this variant occupied a premium position within the Sierra 3500HD lineup, targeting buyers needing substantial towing and hauling capacity combined with a degree of comfort and refinement. It was part of the fourth generation (GMTK2XX) of the Sierra/Silverado HD platform, known for its increased strength and capability compared to its predecessors.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD IV (GMTK2XX) Double Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (445 Hp) 4WD SRW Automatic |
| Start of production | 2017 |
| End of production | 2019 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 7.7 kg/Hp, 130.1 Hp/tonne |
| Weight-to-torque ratio | 2.8 kg/Nm, 360.8 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 | 29.7 l (31.38 US qt | 26.13 UK qt) |
| Kerb Weight | 3420 kg (7539.81 lbs.) |
| Max. weight | 5262 kg (11600.72 lbs.) |
| Max load | 1842 kg (4060.91 lbs.) |
| Trunk (boot) space – maximum | 2162 l (76.35 cu. ft.) |
| 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 | 6321 mm (248.86 in.) |
| Width including mirrors | 2045 mm (80.51 in.) |
| Height | 1980 mm (77.95 in.) |
| Wheelbase | 4017 mm (158.15 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Minimum turning circle (turning diameter) | 16.2 m (53.15 ft.) |
| Drivetrain Architecture | All wheel drive (4×4). ICE drives rear wheels, front wheels engaged via clutch. |
| Number of gears and type of gearbox | 6 gears, automatic transmission Allison |
| Front suspension | Coil spring, Double wishbone, Transverse stabilizer |
| Rear suspension | Rigid axle suspension, Leaf spring |
| Front brakes | Ventilated discs, 355×40 mm |
| Rear brakes | Ventilated discs, 373×34 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| Tires size | 235/80 R17; 265/70 R18 |
| Wheel rims size | 7.5J x 17; 8J x 18 |
INTRODUCTION
The 2017-2019 GMC Sierra 3500HD Double Cab Long Box with the 6.6L Duramax diesel and Allison automatic transmission was positioned as a workhorse for serious hauling and towing. It built upon the GMTK2XX platform, which introduced a fully-boxed frame and stronger suspension components compared to previous generations. The Double Cab configuration offered a balance between passenger space and bed length, making it suitable for both work crews and families. This particular variant was a step up from the base gasoline engine options, appealing to customers who prioritized diesel torque and longevity.
Powertrain & Engine Architecture
At the heart of this Sierra 3500HD lies the Duramax L5P 6.6-liter turbocharged diesel V8. This engine is a testament to modern diesel technology, featuring a cast iron block, aluminum cylinder heads, and a robust rotating assembly. The L5P utilizes a Bosch common rail fuel injection system capable of extremely high injection pressures, contributing to its impressive power and efficiency. The turbocharger, coupled with an intercooler, provides increased air density for enhanced combustion. The engine employs an overhead valve (OHV) valvetrain, a design choice favored for its durability and low-end torque characteristics.
The engine is mated to the Allison 1000 Series six-speed automatic transmission. This transmission is renowned for its durability and ability to handle the immense torque output of the Duramax engine. The Allison features a torque converter lock-up clutch that engages in higher gears to improve fuel economy and reduce slippage. The transmission is electronically controlled, optimizing shift points based on driving conditions and throttle input.
Driving Characteristics
The 445 horsepower and 910 lb-ft of torque delivered by the Duramax/Allison combination translate into exceptional towing and hauling capabilities. In real-world conditions, this truck feels incredibly capable, even when loaded to its maximum capacity. The Allison transmission provides smooth and confident shifts, and the gear ratios are well-suited for both highway cruising and low-speed towing. Compared to the gasoline engine options, the diesel offers significantly more low-end torque, making it easier to accelerate with a heavy load. While not a sports truck, the Sierra 3500HD provides a stable and controlled driving experience. The automatic transmission, while convenient, doesn’t offer the same level of control as a manual transmission, particularly when engine braking on steep descents.
Equipment & Trim Levels
The Sierra 3500HD Double Cab Long Box with the Duramax engine typically came standard with a well-equipped interior. Features included cloth upholstery, air conditioning, power windows and locks, a basic infotainment system with a touchscreen display, and a rearview camera. Higher trim levels, such as the SLT and Denali, added features like leather upholstery, heated and ventilated seats, a premium audio system, navigation, and advanced safety technologies. Optional extras included a sunroof, upgraded wheels, and various appearance packages.
Chassis & Braking
The GMTK2XX platform features a fully-boxed frame constructed from high-strength steel, providing a solid foundation for the truck. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs leaf springs. This configuration is optimized for load-carrying capacity and stability. Braking duties are handled by ventilated disc brakes at all four corners, providing ample stopping power. An Anti-lock Braking System (ABS) is standard. The rear axle typically featured a single rear wheel (SRW) configuration, although dual rear wheel (DRW) options were available for even greater towing capacity.
Market Reception & Comparison
The Duramax/Allison combination in the Sierra 3500HD was generally well-received by critics and consumers alike. It was praised for its powerful engine, smooth transmission, and impressive towing capabilities. Fuel economy, while not exceptional, was considered reasonable for a heavy-duty truck. Compared to the gasoline engine options, the Duramax offered superior torque and longevity, but at a higher initial cost. Compared to the Ford Super Duty and Ram 3500, the Sierra 3500HD was often seen as a more refined and comfortable option, although some competitors offered slightly higher towing capacities.
Legacy
The Duramax L5P engine and Allison 1000 transmission have proven to be exceptionally reliable powertrains. Well-maintained examples of the 2017-2019 Sierra 3500HD continue to command strong resale values in the used car market. The engine is known for its durability and ability to withstand high mileage. However, potential buyers should be aware of the cost of diesel engine maintenance, which can be higher than that of gasoline engines. The GMTK2XX platform also proved to be robust, with relatively few widespread mechanical issues reported. This generation of Sierra 3500HD remains a popular choice for those seeking a capable and reliable heavy-duty truck.
