The GMC Sierra 3500HD III, specifically the facelifted model produced from 2011 to 2013, represented a significant iteration of GMC’s heavy-duty pickup truck lineage. This variant, characterized by its Extended Cab, Long Box configuration, and the potent 6.6-liter Duramax turbodiesel V8 engine paired with an Allison automatic transmission, was aimed squarely at buyers needing substantial towing and hauling capacity. Positioned as a premium work truck and capable personal vehicle, it occupied the upper echelon of the 3500HD lineup, offering a balance of power, comfort, and durability. The GMT900 platform, upon which it was built, was a cornerstone of GM’s heavy-duty truck strategy for many years, undergoing continuous refinement throughout its production run.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD III (GMT900, facelift 2011) Extended Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (397 Hp) DRW Automatic |
| Start of production | 2011 |
| End of production | 2013 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.5 kg/Hp, 117.7 Hp/tonne |
| Weight-to-torque ratio | 3.3 kg/Nm, 307.4 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 | 3373 kg (7436.19 lbs.) |
| Max. weight | 5908 kg (13024.91 lbs.) |
| Max load | 2535 kg (5588.72 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%) | 7484 kg (16499.4 lbs.) |
| Length | 6337 mm (249.49 in.) |
| Width including mirrors | 2436 mm (95.91 in.) |
| Height | 1966 mm (77.4 in.) |
| Wheelbase | 4018 mm (158.19 in.) |
| Front track | 1748 mm (68.82 in.) |
| Rear (Back) track | 1906 mm (75.04 in.) |
| Ride height (ground clearance) | 221 mm (8.7 in.) |
| Minimum turning circle (turning diameter) | 16.1 m (52.82 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, 355×40 mm |
| Rear brakes | Ventilated discs, 373×34 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| Tires size | 235/80 R17; 265/70 R18 |
INTRODUCTION
The 2011-2013 GMC Sierra 3500HD with the 6.6L Duramax diesel and Allison automatic transmission was a workhorse designed for serious tasks. This generation represented a significant refresh of the GMT900 platform, introducing updated styling, improved interior materials, and enhanced technology. The “HD” designation signifies “Heavy Duty,” indicating its capability for substantial towing and payload. The Extended Cab configuration provided additional passenger space compared to the standard cab, while the Long Box offered a generous cargo bed. The Dual Rear Wheel (DRW) configuration further enhanced stability and load-carrying capacity, making it a popular choice for commercial users and those requiring maximum capability.
Powertrain & Engine Architecture
At the heart of this Sierra 3500HD lay the Duramax LML 6.6-liter V8 turbodiesel engine. This engine, a product of a joint venture between General Motors and Isuzu, was renowned for its durability and torque output. The LML iteration featured a revised turbocharger, improved fuel injection system, and enhanced exhaust gas recirculation (EGR) system compared to its predecessors. The engine utilized a common-rail direct injection system, delivering fuel at extremely high pressures for optimized combustion. The overhead valve (OHV) valvetrain, while seemingly traditional, proved robust and reliable. The Allison 6-speed automatic transmission was specifically engineered to handle the immense torque produced by the Duramax engine. This transmission featured a lock-up torque converter for improved fuel efficiency and a heavy-duty cooling system to prevent overheating under demanding conditions. The transmission’s gear ratios were optimized for both towing and everyday driving, providing a balance of power and efficiency.
Driving Characteristics
The 397 horsepower and 765 lb-ft of torque delivered by the Duramax/Allison combination translated into impressive real-world performance. While not a sports truck, the Sierra 3500HD offered ample power for accelerating with a load or tackling steep grades. The Allison transmission shifted smoothly and decisively, providing seamless power delivery. Compared to the gasoline-powered versions of the Sierra 3500HD, the diesel offered significantly more low-end torque, making it ideal for towing heavy trailers. The DRW configuration enhanced stability, particularly when towing, reducing body roll and improving handling. However, the added weight and length of the truck did make it less nimble in tight spaces. The automatic transmission, while convenient, didn’t offer the same level of control as a manual transmission, but it was well-suited for the intended use case of this truck.
Equipment & Trim Levels
The 2011-2013 Sierra 3500HD offered a range of trim levels, with the specific features varying depending on the chosen configuration. Common standard features included air conditioning, power windows and locks, and a basic audio system. Higher trim levels added features such as leather upholstery, heated seats, a premium audio system, navigation, and a rearview camera. The Extended Cab provided a small rear seat, suitable for occasional passengers. Optional extras included a trailer brake controller, a fifth-wheel hitch, and various appearance packages. The interior design was functional and durable, with a focus on practicality rather than luxury.
Chassis & Braking
The Sierra 3500HD’s chassis was designed to withstand the stresses of heavy-duty use. The front suspension featured an independent torsion bar setup with double wishbones, providing a comfortable ride and good handling. The rear suspension utilized a traditional leaf spring design, offering robust 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, enhancing safety and control. The DRW configuration featured larger brakes and a wider track width, further improving braking performance and stability.
Market Reception & Comparison
The 2011-2013 GMC Sierra 3500HD with the Duramax diesel and Allison automatic received generally positive reviews from critics. It was praised for its powerful engine, smooth transmission, and impressive towing and hauling capabilities. Fuel economy, while not exceptional, was considered reasonable for a heavy-duty truck. Compared to the 6.0L gasoline V8 versions, the Duramax diesel offered significantly better fuel economy and torque. The Sierra 3500HD competed directly with the Ford Super Duty and Ram Heavy Duty trucks, and was often seen as a strong contender in terms of capability and reliability.
Legacy
The Duramax LML engine and Allison transmission pairing proved to be exceptionally durable, and many examples of the 2011-2013 Sierra 3500HD remain on the road today. These trucks have earned a reputation for reliability and longevity, making them popular choices in the used truck market. While maintenance costs can be higher than those of gasoline-powered trucks, the Duramax engine’s long lifespan and strong resale value often offset these expenses. The GMT900 platform, while superseded by newer designs, remains a testament to GM’s commitment to building capable and durable heavy-duty trucks.
