The GMC Sierra 2500HD III, specifically the Crew Cab Long Box configuration 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 2011 to 2014 as part of the GMT900 platform’s facelift, this variant was aimed at buyers needing substantial towing and hauling capacity combined with a degree of interior comfort. It occupied a premium position within the 2500HD lineup, offering a powerful diesel option alongside gasoline engines, and catered to customers prioritizing capability over fuel economy.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900, facelift 2011) Crew Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (397 Hp) 4WD Automatic |
| Start of production | 2011 |
| End of production | 2014 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.5 kg/Hp, 117.5 Hp/tonne |
| Weight-to-torque ratio | 3.3 kg/Nm, 307 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) |
| Maximum engine speed | 3000 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 | 24 l (25.36 US qt | 21.12 UK qt) |
| Kerb Weight | 3378 kg (7447.22 lbs.) |
| Max. weight | 4536 kg (10000.17 lbs.) |
| Max load | 1158 kg (2552.95 lbs.) |
| Trunk (boot) space – maximum | 2138 l (75.5 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 | 6581 mm (259.09 in.) |
| Width including mirrors | 2032 mm (80 in.) |
| Height | 1984 mm (78.11 in.) |
| Wheelbase | 4018 mm (158.19 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Ride height (ground clearance) | 208 mm (8.19 in.) |
| Minimum turning circle (turning diameter) | 16.7 m (54.79 ft.) |
| Drivetrain Architecture | All wheel drive (4×4). ICE drives rear wheels, front wheels engaged via clutch. |
| Drive wheel | All wheel drive (4×4) |
| Number of gears and type of gearbox | 6 gears, automatic transmission Allison |
| Front suspension | Independent torsion bar, double wishbone |
| Rear suspension | Rigid axle suspension, Leaf spring |
| Front brakes | Ventilated discs, 350×40 mm |
| Rear brakes | Ventilated discs, 360×34 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| 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 |
INTRODUCTION
The 2011-2014 GMC Sierra 2500HD Crew Cab Long Box equipped with the 6.6L Duramax diesel and Allison automatic transmission was a cornerstone of GMC’s heavy-duty truck offerings. Built on the GMT900 platform, this generation represented a significant upgrade in terms of capability, refinement, and technology compared to its predecessors. The facelift in 2011 brought revised styling, improved interior materials, and enhanced features. This particular configuration was positioned as a premium work truck, appealing to owners who required substantial towing and payload capacity but also desired a comfortable and well-equipped cabin for daily use. It was a direct competitor to Ford’s Super Duty and Ram’s heavy-duty trucks.
Powertrain & Engine Architecture
The heart of this Sierra 2500HD is the Duramax LML 6.6-liter turbocharged diesel V8. This engine, a significant evolution of the previous LBZ and LMM Duramax engines, featured a redesigned combustion chamber, improved fuel injectors, and a more efficient turbocharger. The LML produced 397 horsepower at 3000 rpm and a massive 765 lb-ft (1037 Nm) of torque at 1600 rpm. The engine utilized a common-rail direct fuel injection system, delivering highly pressurized fuel directly into the cylinders for optimal combustion. The valvetrain employed an overhead valve (OHV) configuration, known for its durability and simplicity.
Paired with the Duramax engine was the Allison 1000 six-speed automatic transmission. This transmission was specifically designed to handle the high torque output of the diesel engine and provide smooth, reliable shifting. The Allison transmission featured a lock-up torque converter for improved fuel efficiency at highway speeds and a heavy-duty cooling system to prevent overheating during demanding use. The transmission’s gear ratios were optimized for both towing and everyday driving, providing ample power across a wide range of speeds.
Driving Characteristics
The 6.6L Duramax/Allison combination in the Sierra 2500HD delivered a driving experience characterized by immense pulling power and a surprisingly refined ride for a heavy-duty truck. The engine’s peak torque was available at a relatively low 1600 rpm, providing effortless acceleration even when towing heavy loads. The Allison transmission shifted smoothly and predictably, contributing to a comfortable driving experience. While not a sports truck, the Sierra 2500HD offered ample power for merging onto highways and passing other vehicles. Compared to the gasoline-powered versions of the 2500HD, the diesel offered significantly more torque and towing capacity, but at the expense of higher initial cost and potentially higher maintenance expenses. Compared to manual transmission equipped Duramax models, the automatic offered convenience, especially in stop-and-go traffic, but some drivers preferred the greater control offered by a manual gearbox.
Equipment & Trim Levels
The Crew Cab Long Box configuration offered a spacious interior with seating for five passengers. Standard features typically included air conditioning, power windows and locks, a tilt steering wheel, and a basic audio system. Higher trim levels, such as the SLT and Denali, added features like leather upholstery, heated and cooled front seats, a premium audio system, navigation, and a rear-seat entertainment system. Optional extras included a sunroof, a spray-in bedliner, and various towing packages. The interior design was functional and durable, with a focus on providing a comfortable and practical environment for both work and family use.
Chassis & Braking
The Sierra 2500HD featured a robust chassis designed to withstand the stresses of heavy-duty use. The front suspension utilized an independent torsion bar setup with double wishbones, providing a comfortable ride and good handling. The rear suspension employed a traditional leaf spring design, offering excellent load-carrying capacity. Braking duties were handled by ventilated disc brakes on all four wheels, providing ample stopping power even when towing heavy loads. An anti-lock braking system (ABS) was standard equipment. The truck’s heavy-duty frame and suspension components contributed to its impressive towing and payload capabilities.
Market Reception & Comparison
The 2011-2014 GMC Sierra 2500HD with the Duramax diesel and Allison automatic received generally positive reviews from automotive critics. It was praised for its powerful engine, smooth transmission, comfortable ride, and spacious interior. However, some critics noted the truck’s high price and relatively low fuel economy. Compared to the gasoline-powered versions, the diesel offered superior towing and hauling capabilities but came with a higher price tag. Compared to its competitors, the Sierra 2500HD was often seen as a well-rounded and capable truck, offering a good balance of performance, comfort, and features.
Legacy
The Duramax LML engine and Allison 1000 transmission have proven to be remarkably durable and reliable powertrains. Well-maintained examples of the 2011-2014 Sierra 2500HD continue to command strong resale values in the used car market. The engine is known for its longevity, and the Allison transmission is widely regarded as one of the most reliable automatic transmissions ever produced. These trucks remain popular choices for owners who need a capable and dependable heavy-duty truck for work or recreational use. Common maintenance items include regular oil changes, fuel filter replacements, and coolant flushes. The LML Duramax, while generally reliable, can be susceptible to issues with the exhaust gas recirculation (EGR) system and the diesel particulate filter (DPF), requiring periodic cleaning or replacement.
