The GMC Sierra 3500HD IV (GMTK2XX) Double Cab Long Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 397 horsepower, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2015 to 2017, this variant occupied a premium position within the Sierra 3500HD lineup, catering to buyers requiring substantial towing and hauling capabilities combined with a degree of comfort and refinement. It was part of the fourth generation of the Sierra/Silverado HD trucks, known as the GMTK2XX platform, which brought substantial improvements in capability, interior space, and technology 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) 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 | 8.6 kg/Hp, 116.3 Hp/tonne |
| Weight-to-torque ratio | 3.3 kg/Nm, 303.8 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 | 3413 kg (7524.38 lbs.) |
| Max. weight | 5908 kg (13024.91 lbs.) |
| Max load | 2495 kg (5500.53 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 | 2438 mm (95.98 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) | 213 mm (8.39 in.) |
| Minimum turning circle (turning diameter) | 16.1 m (52.82 ft.) |
| Drivetrain Architecture | Rear wheel drive |
| 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 positioned as a workhorse for serious hauling and towing. The “Double Cab” configuration offered increased rear-seat space compared to the standard cab, making it suitable for crews, while the “Long Box” provided ample bed length for larger payloads. This particular configuration, with the powerful Duramax engine and robust Allison transmission, was aimed at professionals and enthusiasts who needed a truck capable of handling demanding tasks without sacrificing a reasonable level of comfort and convenience. It built upon the foundation laid by previous Sierra 3500HD generations, incorporating updated styling, improved interior materials, and enhanced technology.
Powertrain & Engine Architecture
At the heart of this Sierra 3500HD lies 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 rotating assembly. The LML generation of the Duramax introduced a revised turbocharger, improved fuel injection system, and enhanced exhaust gas recirculation (EGR) system to meet stricter emissions standards while maintaining impressive power output. The engine utilizes a common-rail direct injection system, delivering fuel at extremely high pressures for optimal combustion efficiency. The overhead valve (OHV) valvetrain, while seemingly traditional, is known for its durability and reliability. The Allison 1000 six-speed automatic transmission is a critical component, specifically engineered to handle the immense torque produced by the Duramax engine. This transmission features a lock-up torque converter for improved fuel efficiency and a heavy-duty cooling system to prevent overheating under strenuous conditions. The transmission’s gear ratios are optimized for both towing and everyday driving, providing a balance between power and efficiency.
Driving Characteristics
The 397 horsepower and 765 lb-ft of torque delivered by the Duramax engine and Allison transmission combination translate into impressive real-world performance. While not a sports truck, the Sierra 3500HD offers strong acceleration, even when heavily loaded. The Allison transmission shifts smoothly and decisively, providing ample power for merging onto highways and climbing steep grades. Compared to the gasoline-powered versions of the Sierra 3500HD, the Duramax diesel offers significantly more low-end torque, making it ideal for towing heavy trailers. The automatic transmission, while convenient, does result in a slight performance deficit compared to the available manual transmission, particularly in terms of responsiveness. However, the Allison’s programming is geared towards maximizing efficiency and minimizing stress on the powertrain.
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 Denali. Standard features often included air conditioning, power windows and locks, a rearview camera, and a basic infotainment system. Higher trims added features like leather upholstery, heated and ventilated front seats, a premium sound system, navigation, and advanced safety technologies. Optional extras included a sunroof, upgraded wheels, and various towing packages. The interior design focused on functionality and durability, with comfortable seating and intuitive controls. The Double Cab configuration provided ample space for five passengers, making it a practical choice for crews or families.
Chassis & Braking
The Sierra 3500HD’s chassis is built for heavy-duty use, featuring a fully boxed frame and robust suspension components. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs leaf springs. The rear axle is a heavy-duty unit designed to withstand significant loads. Braking duties are handled by ventilated disc brakes on all four wheels, providing ample stopping power even when towing. An Anti-lock Braking System (ABS) is standard, enhancing safety and control. The steering system utilizes a recirculating ball mechanism, offering a solid and predictable feel.
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, and impressive towing capacity. Fuel economy, while not exceptional, was considered reasonable for a heavy-duty truck of its size and capability. Compared to the 6.0-liter gasoline V8 and the smaller diesel options, the 6.6L Duramax offered a significant advantage in terms of torque and towing capacity. However, the Duramax engine and Allison transmission came at a higher price point. Reliability was generally good, although some owners reported issues with the emissions control system.
Legacy
The 2015-2017 GMC Sierra 3500HD with the 6.6L Duramax and Allison automatic remains a popular choice in the used truck market. The Duramax engine is known for its longevity and durability, and the Allison transmission is widely regarded as one of the most reliable automatic transmissions ever produced. These trucks continue to command a premium price compared to their gasoline-powered counterparts. With proper maintenance, these powertrains can easily exceed 200,000 miles, making them a sound investment for buyers seeking a capable and reliable heavy-duty truck.
