The GMC Sierra 3500HD IV (GMTK2XX) Double Cab Long Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 397 horsepower and paired with a 4WD Dual Rear Wheel (DRW) automatic transmission, was a key offering in GMC’s heavy-duty truck lineup from 2015 to 2017. This variant represented a balance between capability and usability, targeting customers needing substantial towing and hauling capacity without sacrificing everyday drivability. It sat within the fourth generation of the Sierra 3500HD, known as the GMTK2XX platform, which brought significant improvements in interior refinement, technology, and overall performance 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 (397 Hp) 4WD DRW Automatic |
| Start of production | 2015 |
| End of production | 2017 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.9 kg/Hp, 112.1 Hp/tonne |
| Weight-to-torque ratio | 3.4 kg/Nm, 292.9 Nm/tonne |
| Power | 397 Hp @ 3000 rpm |
| Power per litre | 60.2 Hp/l |
| Torque | 1037 Nm @ 1600 rpm, 764.85 lb.-ft. @ 1600 rpm |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Duramax LML |
| Engine displacement | 6599 cm3, 402.7 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 | 22.4 l, 23.67 US qt | 19.71 UK qt |
| Kerb Weight | 3540 kg, 7804.36 lbs |
| Max. weight | 5908 kg, 13024.91 lbs |
| Max load | 2368 kg, 5220.55 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%) | 9072 kg, 20000.34 lbs |
| Length | 6321 mm, 248.86 in |
| Width including mirrors | 2045 mm, 80.51 in |
| Height | 1972 mm, 77.64 in |
| Wheelbase | 4017 mm, 158.15 in |
| Front track | 1748 mm, 68.82 in |
| Rear (Back) track | 1906 mm, 75.04 in |
| Ride height (ground clearance) | 215 mm, 8.46 in |
| Minimum turning circle (turning diameter) | 16.1 m, 52.82 ft |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels permanently, and the front wheels are driven through an electrically or mechanically operated clutch if necessary. |
| Drive wheel | All wheel drive (4×4) |
| 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, 355×40 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 2015-2017 GMC Sierra 3500HD Double Cab Long Box with the 6.6L Duramax diesel and Allison automatic transmission was a workhorse designed for serious hauling and towing. Positioned as a premium heavy-duty truck, it offered a step up in refinement and features compared to the standard Sierra 1500 and 2500HD models. The “Double Cab” configuration provided a larger rear seat area than the standard cab, making it more suitable for occasional passenger transport, while the “Long Box” bed maximized cargo space. This particular configuration was popular among contractors, ranchers, and anyone needing a powerful and versatile truck for both work and personal use.
Powertrain & Engine Architecture
The heart of this Sierra 3500HD is the Duramax LML 6.6-liter turbocharged diesel V8. This engine is a testament to diesel engineering, featuring a cast iron block, aluminum cylinder heads, and a robust crankshaft. The LML generation of the Duramax introduced a revised turbocharger, improved fuel injection system, and enhanced glow plug system for improved cold-start performance and reduced emissions. The engine utilizes a common-rail direct injection system, delivering fuel at extremely high pressures for optimal combustion. The overhead valve (OHV) valvetrain, while seemingly dated compared to overhead cam designs, proved to be durable and reliable. The Allison 1000 six-speed automatic transmission is renowned for its strength and smoothness. It’s specifically designed to handle the high torque output of the Duramax engine, featuring a lock-up torque converter for improved fuel efficiency at highway speeds. The transmission’s gear ratios are optimized for both towing and everyday driving, providing ample power across a wide range of conditions.
Driving Characteristics
The 397 horsepower and 765 lb-ft of torque delivered by the Duramax engine and Allison transmission combination provide impressive performance. While not a sports truck, the Sierra 3500HD offers strong acceleration, even when heavily loaded. The Allison transmission shifts smoothly and decisively, providing a comfortable driving experience. The 4WD system ensures excellent traction in various conditions, making it capable both on and off-road. Compared to the 6.0L gasoline V8 option, the Duramax diesel offers significantly more torque, making it far superior for towing heavy trailers. The automatic transmission, while convenient, does result in a slight performance deficit compared to the available manual transmission, which allows for more direct control over gear selection. However, the Allison automatic’s durability and ease of use made it the preferred choice for many buyers.
Equipment & Trim Levels
The Sierra 3500HD Double Cab Long Box with the Duramax engine was typically offered in higher trim levels, such as SLE and SLT. Standard features included air conditioning, power windows and locks, a tilt steering wheel, and a basic audio system. Higher trims added features like leather upholstery, heated and ventilated front seats, a premium audio system, navigation, and a rearview camera. Optional extras included a sunroof, upgraded wheels, and various towing packages. The interior design focused on functionality and durability, with comfortable seating and easy-to-use controls. The Double Cab configuration provided ample space for five passengers, making it a practical choice for families or crews.
Chassis & Braking
The Sierra 3500HD features a heavy-duty chassis designed to withstand the stresses of heavy hauling and towing. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs a traditional leaf spring setup. This combination provides a comfortable ride while maintaining excellent load-carrying capacity. The braking system consists of ventilated disc brakes on all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) is standard, enhancing safety and control during emergency braking situations. The DRW configuration (Dual Rear Wheels) significantly increases the truck’s stability and load-carrying capacity, making it ideal for extremely heavy trailers.
Market Reception & Comparison
The GMC Sierra 3500HD with the Duramax diesel and Allison automatic received generally positive reviews from critics. It was praised for its powerful engine, smooth transmission, comfortable ride, and refined interior. Fuel economy, while not exceptional, was considered reasonable for a heavy-duty truck of its size and capability. Compared to the Ford Super Duty and Ram 3500, the Sierra 3500HD was often seen as offering a more refined driving experience and a more upscale interior. However, some critics noted that the GMC’s price was slightly higher than its competitors. The Duramax/Allison combination was consistently lauded for its reliability and longevity, making it a popular choice among buyers seeking a long-lasting work truck.
Legacy
The Duramax LML engine and Allison 1000 transmission have proven to be exceptionally durable and reliable powertrains. Well-maintained examples of the 2015-2017 Sierra 3500HD continue to command strong resale values in the used car market. The engine is known for its ability to accumulate high mileage without major issues, provided it receives regular maintenance, including oil changes and fuel filter replacements. The Allison transmission is equally robust, capable of handling years of heavy use. This particular variant of the Sierra 3500HD remains a popular choice for those seeking a capable and dependable heavy-duty truck that can handle demanding tasks for years to come.
