The GMC Sierra 2500HD III, specifically the Crew Cab Standard Box configuration powered by the 6.6-liter Duramax turbodiesel V8 engine and paired with an Allison automatic transmission, 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 squarely at the American market’s demand for capable, powerful, and comfortable work trucks. It occupied a sweet spot in the 2500HD lineup, offering a substantial increase in capability over the gasoline-powered options while remaining more accessible than the top-tier trims.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900, facelift 2011) Crew Cab Standard Box |
| Type (Engine) | 6.6 Duramax TD V8 (397 Hp) Automatic |
| Start of production | 2011 |
| End of production | 2014 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 5 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.1 kg/Hp, 123.8 Hp/tonne |
| Weight-to-torque ratio | 3.1 kg/Nm, 323.5 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 | 3206 kg (7068.02 lbs.) |
| Max. weight | 4536 kg (10000.17 lbs.) |
| Max load | 1330 kg (2932.15 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 | 6101 mm (240.2 in.) |
| Width including mirrors | 2032 mm (80 in.) |
| Height | 1958 mm (77.09 in.) |
| Wheelbase | 3904 mm (153.7 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Ride height (ground clearance) | 213 mm (8.39 in.) |
| Minimum turning circle (turning diameter) | 15.4 m (50.52 ft.) |
| Drivetrain Architecture | Rear wheel drive |
| Drive wheel | Rear wheel drive |
| 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 is the Duramax LML 6.6-liter V8 turbodiesel. This engine represented a significant evolution of the Duramax design, incorporating a redesigned combustion chamber, improved fuel injection strategies, 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 engine also featured a variable geometry turbocharger (VGT) and an intercooler to maximize power and torque output. The overhead valve (OHV) valvetrain, while traditional, was optimized for durability and low-end torque. Paired with the engine is the Allison 1000 six-speed automatic transmission, renowned for its durability and ability to handle the immense torque produced by the Duramax engine. This transmission featured a lock-up torque converter for improved fuel efficiency at highway speeds and was specifically calibrated for heavy-duty truck applications.
Driving Characteristics
The 6.6L Duramax with the Allison automatic provided a compelling driving experience. While not as overtly sporty as some gasoline-powered trucks, the Sierra 2500HD offered immense pulling power and a relaxed cruising demeanor. The Allison transmission’s gear ratios were well-suited for both towing and everyday driving, providing smooth and confident shifts. The 1600 rpm peak torque meant that the truck felt strong and responsive even at lower engine speeds. Compared to the 6.0L gasoline V8 option, the Duramax offered significantly more torque and better fuel economy, especially when towing. Compared to higher-output Duramax variants, this 397 hp version offered a balance between power and affordability, making it a popular choice for those who needed a capable truck without the premium price tag of the higher trims.
Equipment & Trim Levels
The Crew Cab Standard Box configuration typically came well-equipped, even in base trims. Standard features generally included air conditioning, power windows and locks, a basic audio system, and vinyl upholstery. The Sierra 2500HD offered several trim levels, with this Duramax/Allison combination available in SLE and SLT trims. SLE models added features like chrome exterior trim, upgraded cloth upholstery, and a better audio system. SLT models further enhanced the experience with leather upholstery, heated front seats, a premium audio system, and additional convenience features. Optional extras included a navigation system, a rear-seat entertainment system, and various towing packages.
Chassis & Braking
The Sierra 2500HD’s chassis was designed for heavy-duty use. It featured a fully boxed frame for increased rigidity and durability. 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, optimized for 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 rear axle ratios varied depending on the specific configuration, influencing both towing capacity 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 comfortable ride. Fuel economy, while not exceptional, was considered good for a heavy-duty truck. Compared to the Ford Super Duty and Ram 2500, the Sierra 2500HD offered a competitive combination of features, performance, and reliability. Some critics noted that the interior design was somewhat dated compared to its rivals, but the overall build quality and durability were highly regarded.
Legacy
The Duramax LML engine and Allison transmission pairing have proven to be exceptionally durable and reliable. Properly maintained examples of this powertrain can easily exceed 200,000 miles. On the used car market, these Sierra 2500HDs remain popular choices for those seeking a capable and dependable work truck. They command a premium price compared to gasoline-powered models, reflecting the Duramax engine’s reputation for longevity and performance. The 2011-2014 facelifted GMT900 platform represents a refined and capable iteration of GMC’s heavy-duty truck lineage, solidifying the Sierra 2500HD’s position as a leading contender in the American truck market.
