The GMC Sierra 2500HD III, specifically the facelifted model produced from 2011 to 2014, represented a significant evolution in GMC’s heavy-duty truck lineup. This variant, featuring an Extended Cab with a Standard Box, coupled with the 6.6-liter Duramax Turbo Diesel V8 engine producing 397 horsepower and paired with a 4WD automatic transmission, was positioned as a workhorse for those needing substantial towing and hauling capacity. It built upon the GMT900 platform, offering a blend of rugged capability and improved refinement compared to its predecessors. This configuration aimed to balance power, efficiency, and usability for both commercial and personal applications.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900, facelift 2011) Extended Cab Standard 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 | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.2 kg/Hp, 122.1 Hp/tonne |
| Weight-to-torque ratio | 3.1 kg/Nm, 318.9 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) |
| 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 | 3252 kg (7169.43 lbs.) |
| Max. weight | 4536 kg (10000.17 lbs.) |
| Max load | 1284 kg (2830.74 lbs.) |
| Trunk (boot) space – maximum | 1718 l (60.67 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 | 5857 mm (230.59 in.) |
| Width including mirrors | 2032 mm (80 in.) |
| Height | 1979 mm (77.91 in.) |
| Wheelbase | 3663 mm (144.21 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Ride height (ground clearance) | 216 mm (8.5 in.) |
| Minimum turning circle (turning diameter) | 14.6 m (47.9 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 | 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 |
Powertrain & Engine Architecture
The heart of this Sierra 2500HD variant is the 6.6-liter Duramax LML turbo diesel V8 engine. This engine represented a significant upgrade over previous Duramax iterations, incorporating a redesigned combustion chamber, improved fuel injection system, and a more robust cooling system. The LML utilized a common-rail direct injection system, delivering fuel at extremely high pressures for optimized combustion efficiency and reduced emissions. The turbocharger, coupled with an intercooler, provided increased air intake, boosting power and torque output. The engine’s OHV valvetrain, while traditional, was engineered for durability and reliability. The Allison 6-speed automatic transmission was specifically calibrated to handle the engine’s substantial torque, providing smooth and efficient gear changes. This transmission featured a lock-up torque converter for improved fuel economy at highway speeds.
Driving Characteristics
The 397 horsepower and 765 lb-ft of torque delivered by the Duramax engine and Allison transmission combination resulted in impressive performance. While not a sports truck, the Sierra 2500HD offered strong acceleration, even when heavily loaded. The automatic transmission’s gear ratios were optimized for towing, providing ample low-end torque for pulling heavy trailers. Compared to the gasoline-powered versions of the Sierra 2500HD, the diesel offered significantly more torque and better fuel economy, especially under load. The 4WD system provided excellent traction in various conditions, making it suitable for both on-road and off-road use. However, the added weight of the diesel engine and 4WD system did impact handling, making it feel less nimble than lighter-duty trucks.
Equipment & Trim Levels
The Extended Cab Standard Box configuration offered a practical balance between passenger space and cargo capacity. Standard features typically included air conditioning, power windows and locks, a basic audio system, and vinyl upholstery. Higher trim levels, such as the SLT and Denali, added features like leather upholstery, heated seats, a premium audio system, navigation, and various convenience features. Optional extras included a sunroof, upgraded wheels, and a trailer brake controller. The interior design was functional and durable, prioritizing practicality over luxury.
Chassis & Braking
The Sierra 2500HD’s chassis was built for heavy-duty use, featuring a robust frame and heavy-duty suspension components. The front suspension utilized an independent torsion bar setup with double wishbones, while the rear suspension employed a traditional leaf spring design. This configuration provided a comfortable ride, even when carrying heavy loads. The braking system consisted of ventilated discs on all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) was standard, enhancing safety and control. The rear axle ratios were selected to optimize towing performance and fuel economy.
Market Reception & Comparison
The 2011-2014 GMC Sierra 2500HD with the 6.6L Duramax and Allison automatic was generally well-received by critics and consumers alike. It was praised for its powerful engine, smooth transmission, and impressive towing capacity. Compared to the gasoline-powered Sierra 2500HD, the diesel version offered superior fuel economy and torque, making it a popular choice for those who frequently towed or hauled heavy loads. However, the diesel engine came with a higher price tag and potentially higher maintenance costs. Compared to competitors like the Ford Super Duty and Ram 2500, the Sierra 2500HD offered a competitive combination of features, performance, and reliability.
Legacy
The Duramax LML engine and Allison transmission pairing proved to be exceptionally durable and reliable. Properly maintained examples of this powertrain continue to operate reliably today, often exceeding 200,000 miles. The 2011-2014 Sierra 2500HD remains a popular choice in the used truck market, commanding relatively high prices due to its reputation for dependability and capability. While newer heavy-duty trucks offer more advanced technology and features, this generation represents a sweet spot for those seeking a proven and capable work truck at a reasonable price. The LML Duramax engine is still considered one of the most robust and reliable diesel engines ever produced, solidifying its place in the history of American trucks.
