The GMC Sierra 3500HD IV (GMTK2XX) Regular 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 configuration represented a robust work truck solution, positioned between the lighter-duty 2500HD models and the most heavily equipped 3500HD trims. It catered to owners needing substantial towing and payload capacity for commercial or demanding personal use.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD IV (GMTK2XX) Regular 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 | 2 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.5 kg/Hp, 118.1 Hp/tonne |
| Weight-to-torque ratio | 3.2 kg/Nm, 308.4 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 | 3362 kg, 7411.94 lbs |
| Max. weight | 5908 kg, 13024.91 lbs |
| Max load | 2546 kg, 5612.97 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 | 5699 mm, 224.37 in |
| Width including mirrors | 2438 mm, 95.98 in |
| Height | 1967 mm, 77.44 in |
| Wheelbase | 3393 mm, 133.58 in |
| Front track | 1748 mm, 68.82 in |
| Rear (Back) track | 1906 mm, 75.04 in |
| Ride height (ground clearance) | 205 mm, 8.07 in |
| Minimum turning circle (turning diameter) | 14 m, 45.93 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, 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 with the 6.6L Duramax diesel and Allison automatic transmission represented the fourth generation (GMTK2XX) of GMC’s heavy-duty truck platform. This generation, introduced in 2015, brought significant improvements in refinement, capability, and technology compared to its predecessor. The Regular Cab Long Box configuration, combined with the DRW setup, was specifically designed for customers prioritizing maximum towing and hauling capacity. This truck was a mainstay for contractors, farmers, and anyone needing a serious workhorse.
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 rotating assembly. The LML iteration of the Duramax introduced a revised turbocharger, improved fuel injection system, and enhanced exhaust gas recirculation (EGR) system for increased efficiency and reduced emissions. The engine utilizes a common-rail direct fuel injection system, delivering fuel at extremely high pressures for optimal combustion. The valvetrain employs an overhead valve (OHV) configuration, known for its durability and simplicity. The Allison 1000 six-speed automatic transmission is specifically designed to handle the immense torque output of the Duramax engine. This transmission features a lock-up torque converter for improved fuel economy and a heavy-duty cooling system to prevent overheating under demanding conditions.
Driving Characteristics
The 397 horsepower and 765 lb-ft of torque delivered by the Duramax engine, coupled with the Allison automatic, provided substantial pulling power. While not as quick off the line as gasoline-powered trucks, the Sierra 3500HD excelled in situations requiring low-end grunt. The Allison transmission’s gear ratios were optimized for towing, providing smooth and confident shifts even when hauling heavy loads. Compared to the 6.0L gasoline V8 option, the Duramax offered significantly more torque, making it the preferred choice for serious towing. The DRW configuration further enhanced stability and load-carrying capacity, but also resulted in a wider stance, requiring more careful maneuvering in tight spaces. The automatic transmission, while convenient, didn’t offer the same level of control as a manual transmission, but it was well-suited for long-distance hauling and everyday driving.
Equipment & Trim Levels
The Sierra 3500HD Regular Cab Long Box with the Duramax engine typically came standard with features like air conditioning, power windows and locks, and a basic audio system. Higher trim levels, such as the SLE and Denali, added features like leather upholstery, heated seats, a premium audio system, and advanced safety technologies. The interior of the Regular Cab was functional and durable, prioritizing practicality over luxury. Optional extras included a navigation system, a rear vision camera, and various towing packages. The Long Box bed provided ample cargo space, and a variety of bed liners and tie-down systems were available.
Chassis & Braking
The Sierra 3500HD’s chassis was designed for heavy-duty use. It featured a fully boxed frame, providing exceptional strength and rigidity. The front suspension utilized coil springs and a double wishbone design, while the rear suspension employed leaf springs. The DRW configuration featured a wider rear axle for increased stability. Braking duties were handled by ventilated disc brakes on all four wheels, providing ample stopping power even when heavily loaded. An Anti-lock Braking System (ABS) was standard. The steering system utilized a recirculating ball mechanism, offering a solid and predictable feel.
Market Reception & Comparison
The GMC Sierra 3500HD with the Duramax engine consistently received positive reviews for its towing capacity, durability, and refined driving experience. Critics praised the engine’s power and efficiency, as well as the Allison transmission’s smooth operation. Compared to the Ford Super Duty and Ram 3500, the Sierra 3500HD was often seen as offering a more comfortable ride and a more upscale interior. Fuel economy, while respectable for a heavy-duty truck, was still relatively low compared to lighter-duty vehicles. Reliability was generally good, although some owners reported issues with the EGR system and diesel particulate filter.
Legacy
The Duramax LML engine and Allison transmission combination proved to be exceptionally durable and reliable. These trucks continue to hold their value well in the used car market, particularly those that have been well-maintained. The 2015-2017 Sierra 3500HD remains a popular choice for buyers seeking a capable and dependable heavy-duty truck. The LML Duramax is considered one of the most robust diesel engines ever produced, and its longevity is a testament to its engineering. Regular maintenance, including oil changes and filter replacements, is crucial for ensuring the long-term reliability of this powertrain.
