The GMC Sierra 2500HD IV (GMTK2XX) Double Cab Standard Box, equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 397 horsepower and paired with an Allison automatic transmission, was a key offering in GMC’s heavy-duty pickup truck lineup from 2015 to 2017. This configuration represented a balance between capability and usability, targeting customers needing substantial towing and hauling capacity without the extreme bulk of the crew cab models. It occupied a middle ground within the 2500HD range, positioned above the gasoline-powered engines and below the more specialized configurations like those geared towards maximum towing.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD IV (GMTK2XX) Double Cab Standard Box |
| Type (Engine) | 6.6 Duramax TD V8 (397 Hp) 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 | 7.9 kg/Hp, 125.9 Hp/tonne |
| Weight-to-torque ratio | 3 kg/Nm, 328.9 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 | 3153 kg (6951.18 lbs.) |
| Max. weight | 4536 kg (10000.17 lbs.) |
| Max load | 1383 kg (3048.99 lbs.) |
| Trunk (boot) space – maximum | 1728 l (61.02 cu. ft.) |
| Fuel tank capacity | 136 l (35.93 US gal | 29.92 UK gal) |
| Permitted trailer load with brakes (12%) | 5897 kg (13000.66 lbs.) |
| Length | 5842 mm (230 in.) |
| Width including mirrors | 2045 mm (80.51 in.) |
| Height | 1984 mm (78.11 in.) |
| Wheelbase | 3662 mm (144.17 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Ride height (ground clearance) | 218 mm (8.58 in.) |
| Minimum turning circle (turning diameter) | 15 m (49.21 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, 360×34 mm |
| Tires size | 245/75 R17; 265/70 R17; 265/70 R18; 265/60 R20 |
| Wheel rims size | 7.5J x 17; 8J x 18; 8.5J x 20 |
Powertrain & Engine Architecture
The heart of this Sierra 2500HD variant is the Duramax LML 6.6-liter turbocharged diesel V8. This engine, a cornerstone of GMC’s heavy-duty lineup, is known for its robust construction and high torque output. The LML generation, introduced in 2011, featured a revised turbocharger, improved fuel injection system, and enhanced cooling compared to its predecessors. The engine utilizes a common-rail direct injection system, delivering fuel at extremely high pressures for optimized combustion. The overhead valve (OHV) valvetrain, while seemingly dated, is favored for its durability and simplicity in a high-stress application. The Allison 1000 six-speed automatic transmission is specifically designed to handle the immense torque produced by the Duramax engine. It features a lock-up torque converter for improved fuel efficiency at highway speeds and heavy-duty internal components for reliability under demanding conditions. The transmission’s programming is tuned to provide smooth shifts while maximizing power delivery for towing and hauling.
Driving Characteristics
The 397 horsepower and 765 lb-ft of torque delivered by this combination translate to impressive real-world performance. While not as quick off the line as lighter-duty trucks, the Sierra 2500HD excels in situations requiring substantial pulling power. The Allison transmission’s gear ratios are optimized for towing, providing ample torque in lower gears and maintaining reasonable engine speeds at highway speeds. Compared to the gasoline-powered 6.0-liter V8, the Duramax diesel offers significantly more torque, making it the preferred choice for those regularly 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’s smooth shifting and ease of use make it a popular choice for most drivers.
Equipment & Trim Levels
The Double Cab Standard Box configuration typically came with a solid array of standard features. Interior appointments generally included cloth upholstery, though leather was available as an option. Standard equipment often included air conditioning, power windows and locks, a basic audio system, and a tilt steering wheel. Higher trim levels, such as the SLT and Denali, added features like leather upholstery, heated seats, a premium audio system, navigation, and advanced safety technologies. The Standard Box bed length offered a practical balance between cargo capacity and maneuverability. Optional extras included a trailer brake controller, a fifth-wheel hitch, and various bed accessories.
Chassis & Braking
The Sierra 2500HD’s chassis is built for heavy-duty use. The front suspension utilizes coil springs and a double wishbone design, while the rear suspension employs a traditional leaf spring setup. This configuration provides a comfortable ride while maintaining excellent load-carrying capacity. Braking duties are handled by ventilated disc brakes on all four wheels, providing ample stopping power even when heavily loaded. An Anti-lock Braking System (ABS) is standard. The rear axle ratios varied depending on the specific configuration, influencing both towing capacity and fuel economy.
Market Reception & Comparison
The 6.6-liter Duramax diesel with the Allison automatic transmission was widely praised by automotive critics for its power, reliability, and fuel efficiency. While the initial cost was higher than gasoline-powered models, the Duramax offered significantly lower operating costs for those who drove high mileage or frequently towed heavy loads. Compared to the Ford Super Duty and Ram 2500/3500, the Sierra 2500HD was often seen as offering a refined driving experience and a well-appointed interior. Fuel economy, while not exceptional, was competitive within the heavy-duty truck segment.
Legacy
The Duramax LML engine paired with the Allison transmission has proven to be a remarkably durable powertrain. Properly maintained examples of the 2015-2017 Sierra 2500HD continue to command strong resale values in the used car market. The engine is known for its longevity, with many units exceeding 200,000 miles with minimal issues. Common maintenance items include regular oil changes, fuel filter replacements, and occasional injector cleaning. The combination of power, reliability, and capability has cemented the Sierra 2500HD’s reputation as a workhorse truck, making it a popular choice for both commercial and personal use.
