The GMC Sierra 2500HD III, specifically the facelifted version produced from 2011 to 2014, represented a significant iteration of GMC’s heavy-duty pickup truck line. This generation, designated GMT900, offered a robust platform for demanding tasks, and the Regular Cab Long Box configuration with the 6.6-liter Duramax turbodiesel V8 engine and Allison automatic transmission was a popular choice for those needing substantial towing and hauling capacity. This particular variant occupied a sweet spot in the lineup, offering a powerful and capable work truck without the added expense of higher trim levels.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900, facelift 2011) Regular Cab Long 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 | 2 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 7.4 kg/Hp, 135.3 Hp/tonne |
| Weight-to-torque ratio | 2.8 kg/Nm, 353.4 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) |
| 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 | 2934 kg (6468.36 lbs.) |
| Max. weight | 4491 kg (9900.96 lbs.) |
| Max load | 1557 kg (3432.6 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 | 5715 mm (225 in.) |
| Width including mirrors | 2032 mm (80 in.) |
| Height | 1971 mm (77.6 in.) |
| Wheelbase | 3369 mm (132.64 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1709 mm (67.28 in.) |
| Ride height (ground clearance) | 231 mm (9.09 in.) |
| Minimum turning circle (turning diameter) | 13.7 m (44.95 ft.) |
| Drivetrain Architecture | 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 |
| 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 Regular Cab Long Box with the 6.6L Duramax diesel and Allison automatic transmission was a workhorse designed for serious hauling and towing. Part of the GMT900 generation, this truck benefited from a mid-cycle refresh that included styling updates and improvements to the interior. The Regular Cab configuration, paired with the long bed, catered to customers prioritizing functionality over passenger space. This combination was particularly popular with tradesmen, farmers, and those frequently needing to transport large loads. It sat below the Denali trim in terms of luxury, but offered comparable capability.
Powertrain & Engine Architecture
The heart of this Sierra 2500HD is the Duramax LML 6.6-liter V8 turbodiesel engine. This engine represented a significant evolution of the Duramax design, incorporating a redesigned combustion chamber, improved fuel injection system, and a more efficient turbocharger. The LML utilized a common-rail direct injection system, delivering fuel at extremely high pressures for optimized combustion. The engine also featured a variable geometry turbocharger (VGT) to enhance low-end torque and improve overall responsiveness. The overhead valve (OHV) valvetrain, while traditional, proved durable and reliable.
The Allison 1000 six-speed automatic transmission was specifically engineered to handle the immense torque output of the Duramax engine. Known for its robustness and smooth shifting, the Allison transmission featured a torque converter lock-up clutch to improve fuel efficiency at highway speeds. The transmission’s gear ratios were optimized for both towing and everyday driving, providing a balance between power and economy. First gear was geared low for maximizing pulling power, while higher gears allowed for comfortable cruising.
Driving Characteristics
The 397 horsepower and 765 lb-ft of torque delivered by this powertrain combination resulted in impressive performance, even when heavily loaded. While not as quick as gasoline-powered trucks, the Duramax offered a broad, flat torque curve, making it exceptionally capable for towing. Acceleration was brisk, and the Allison transmission shifted smoothly and predictably. The truck felt planted and stable, even with a substantial load in the bed or a trailer attached. Compared to the 6.0L gasoline V8 option, the Duramax provided significantly more torque and better fuel economy, especially under load. Compared to higher-output Duramax variants, this 397hp version offered a slightly more refined driving experience, with less engine noise and vibration.
Equipment & Trim Levels
The base Regular Cab configuration typically included features like air conditioning, a basic audio system, and vinyl upholstery. However, even in its most basic form, the Sierra 2500HD offered a functional and durable interior. Optional equipment included power windows and locks, a premium audio system, and upgraded cloth or leather upholstery. The work truck (WT) trim was the most common for this powertrain, focusing on affordability and durability. Higher trims, like the SLE and SLT, added more comfort and convenience features, but at a higher price point.
Chassis & Braking
The GMT900 chassis was designed for heavy-duty use, featuring a fully boxed frame and robust suspension components. 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 at all four corners, providing ample stopping power. An Anti-lock Braking System (ABS) was standard equipment. The rear axle ratios varied depending on the specific configuration, with options available to optimize for towing or fuel economy.
Market Reception & Comparison
The 2011-2014 GMC Sierra 2500HD with the Duramax diesel and Allison automatic received generally positive reviews. Critics praised its powerful engine, smooth transmission, and impressive towing capacity. 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 was often seen as offering a good balance of capability, comfort, and value. The Duramax engine was consistently ranked among the best diesel engines in the heavy-duty truck segment. Reliability was generally good, although some owners reported issues with the diesel particulate filter (DPF) system.
Legacy
The Duramax LML engine and Allison transmission combination proved to be exceptionally durable and reliable. These trucks continue to be popular on the used market, commanding relatively high prices due to their proven track record. The LML Duramax is known for its longevity and ability to withstand high mileage. Proper maintenance, including regular oil changes and DPF servicing, is crucial for ensuring the long-term reliability of this powertrain. Today, these Sierra 2500HDs remain a viable option for those needing a capable and dependable heavy-duty truck.
