The GMC Sierra 3500HD III, specifically the Crew Cab Long Box configuration with the 6.6-liter Duramax Turbo Diesel V8 engine paired with an Allison automatic transmission, represents a significant iteration in GMC’s heavy-duty truck lineage. Produced from 2011 to 2013 as part of the GMT900 platform’s facelift, this variant was aimed squarely at the demanding needs of owners requiring substantial towing and hauling capabilities. It occupied a premium position within the Sierra 3500HD lineup, offering a balance of power, refinement, and practicality for both work and personal use. This model year saw updates to the interior and exterior styling, along with refinements to the Duramax engine and Allison transmission, enhancing its overall appeal and performance.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD III (GMT900, facelift 2011) Crew Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (397 Hp) SRW Automatic |
| Start of production | 2011 |
| End of production | 2013 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.2 kg/Hp, 122.7 Hp/tonne |
| Weight-to-torque ratio | 3.1 kg/Nm, 320.5 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 | 3236 kg (7134.16 lbs.) |
| Max. weight | 5171 kg (11400.1 lbs.) |
| Max load | 1935 kg (4265.94 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 | 2436 mm (95.91 in.) |
| Height | 1979 mm (77.91 in.) |
| Wheelbase | 4260 mm (167.72 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) | 16.7 m (54.79 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 |
Powertrain & Engine Architecture
The heart of this Sierra 3500HD is the 6.6-liter Duramax LML turbo diesel V8. This engine represents a significant evolution of the Duramax design, incorporating a revised combustion chamber, stronger connecting rods, and an improved cooling system. The LML featured a high-pressure common rail fuel injection system, delivering fuel at extremely high pressures for optimized combustion and reduced emissions. The engine’s valvetrain utilizes an overhead valve (OHV) configuration, known for its durability and simplicity. A variable geometry turbocharger and intercooler work in tandem to maximize power and torque across a broad RPM range. The Allison 6-speed automatic transmission is specifically tuned for the heavy-duty application, providing smooth and reliable shifting even under extreme loads. This transmission is renowned for its durability and ability to handle the substantial torque output of the Duramax engine.
Driving Characteristics
The 397 horsepower and 765 lb-ft of torque delivered by this powertrain configuration translate into impressive real-world performance. While not as overtly quick as lighter-duty trucks, the Sierra 3500HD with the Duramax and Allison excels at towing and hauling. The Allison transmission’s gear ratios are optimized for maximizing torque at lower RPMs, providing strong acceleration even with a heavy load. Compared to the 6.0L gasoline V8 option, the Duramax offers significantly more torque and better fuel economy, especially when towing. Compared to the 1.9L TDI versions, the Duramax offers a much higher towing capacity and overall power, but at the cost of fuel economy and a higher initial purchase price. The ride quality, while firm due to the heavy-duty suspension, is surprisingly comfortable, especially in the Crew Cab configuration.
Equipment & Trim Levels
The Crew Cab Long Box configuration typically came standard with features like air conditioning, power windows and locks, a premium audio system, and cloth upholstery. Higher trim levels, such as the SLT and Denali, added features like leather upholstery, heated and cooled seats, a navigation system, and a rear-seat entertainment system. Optional extras included a sunroof, upgraded audio systems, and various towing packages. The interior design focused on functionality and durability, with large, easy-to-use controls and ample storage space.
Chassis & Braking
The Sierra 3500HD’s chassis is built around a robust fully boxed frame, designed to withstand the stresses of heavy-duty use. The front suspension utilizes an independent torsion bar setup with double wishbones, providing a comfortable ride and good handling. The rear suspension employs a traditional leaf spring design, optimized for load-carrying capacity. Braking duties are handled by ventilated disc brakes on all four wheels, providing ample stopping power even with a heavy load. An Anti-lock Braking System (ABS) is standard, enhancing safety and control. The rear axle was typically a single rear wheel (SRW) configuration, though dual rear wheel (DRW) options were available for even greater towing capacity.
Market Reception & Comparison
The 2011-2013 GMC Sierra 3500HD with the Duramax and Allison combination received generally positive reviews from automotive critics. It was praised for its powerful engine, smooth transmission, and impressive towing capabilities. Fuel economy, while not exceptional, was considered good for a heavy-duty truck. Compared to its competitors, such as the Ford Super Duty and Ram 3500, the Sierra 3500HD offered a compelling combination of performance, refinement, and value. Some critics noted that the interior, while functional, lacked the luxurious appointments found in some competing models.
Legacy
The Duramax LML engine and Allison transmission pairing has proven to be exceptionally durable and reliable. These trucks continue to hold their value well in the used car market, and are highly sought after by owners who require a capable and dependable heavy-duty truck. With proper maintenance, these powertrains can easily exceed 200,000 miles. The 2011-2013 Sierra 3500HD represents a sweet spot in the GMT900 generation, offering a refined and capable truck that continues to serve owners well today. The LML Duramax is considered one of the most reliable and powerful diesel engines ever produced by General Motors.
