The GMC Sierra 3500HD III, produced between 2007 and 2010, represented a significant evolution in GMC’s heavy-duty truck lineup. Part of the GMT900 generation, this iteration of the Sierra 3500HD was designed to offer increased capability, refinement, and a more robust diesel powertrain option. The Crew Cab Long Box configuration, paired with the 6.6-liter Duramax turbodiesel V8 engine producing 365 horsepower and 895 lb-ft of torque, and a six-speed Allison automatic transmission, positioned this truck as a premium workhorse aimed at buyers needing substantial towing and hauling capacity. This specific combination was a popular choice for those requiring a powerful and comfortable truck for both commercial and personal use.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD III (GMT900) Crew Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (365 Hp) 4WD SRW Automatic |
| Start of production | 2007 |
| End of production | 2010 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 4 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.7 kg/Hp, 115.1 Hp/tonne |
| Weight-to-torque ratio | 3.5 kg/Nm, 282.2 Nm/tonne |
| Power | 365 Hp @ 3200 rpm |
| Power per litre | 55.3 Hp/l |
| Torque | 895 Nm @ 1600 rpm, 660.12 lb.-ft. @ 1600 rpm |
| Maximum engine speed | 3450 rpm |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Duramax LMM |
| 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 | 16.8:1 |
| 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 | 3172 kg, 6993.06 lbs |
| Max. weight | 4490 kg, 9898.76 lbs |
| Max load | 1318 kg, 2905.69 lbs |
| Trunk (boot) space – maximum | 2170 l, 76.63 cu. ft |
| Fuel tank capacity | 129 l, 34.08 US gal | 28.38 UK gal |
| Permitted trailer load with brakes (12%) | 5897 kg, 13000.66 lbs |
| Length | 6572 mm, 258.74 in |
| Width including mirrors | 2436 mm, 95.91 in |
| Height | 1934 mm, 76.14 in |
| Wheelbase | 4242 mm, 167.01 in |
| Front track | 1742 mm, 68.58 in |
| Rear (Back) track | 1676 mm, 65.98 in |
| Ride height (ground clearance) | 233 mm, 9.17 in |
| Minimum turning circle (turning diameter) | 16.8 m, 55.12 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, 325×38 mm |
| Rear brakes | Ventilated discs, 325×30 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| Tires size | 265/75 R16; 265/70 R17; 225/75 R17 |
| Wheel rims size | 6.5J x 17; 7J x 16; 7.5J x 17 |
Powertrain & Engine Architecture
The heart of this Sierra 3500HD variant is the Duramax LMM 6.6-liter V8 diesel engine. This engine represented a refinement of the previous LBZ Duramax, incorporating a more robust crankshaft, redesigned pistons, and an improved cooling system. The LMM utilized a common-rail fuel injection system, delivering fuel at extremely high pressures for optimized combustion and reduced emissions. The engine also featured a variable geometry turbocharger (VGT) and an intercooler to maximize power and efficiency. The OHV valvetrain, while traditional, was known for its durability and reliability. The Allison 1000 six-speed automatic transmission was specifically designed to handle the high torque output of the Duramax engine. It featured a lock-up torque converter for improved fuel economy and a heavy-duty cooling system to prevent overheating during demanding tasks.
Driving Characteristics
The 365 horsepower and 895 lb-ft of torque delivered by the Duramax/Allison combination provided impressive performance for a heavy-duty truck. While not as quick as gasoline-powered alternatives, the Sierra 3500HD offered substantial pulling power and a relaxed driving experience. The Allison transmission’s six gears allowed for a wide range of ratios, optimizing both fuel economy at highway speeds and low-end torque for towing. Compared to the 1.8L gasoline engine options available in the Sierra 1500, this diesel variant was in a different league, prioritizing capability over outright acceleration. The automatic transmission, while convenient, did result in a slight power loss compared to the available manual transmission, but the trade-off in ease of use was often preferred by buyers.
Equipment & Trim Levels
The Crew Cab Long Box configuration was typically offered in higher trim levels, such as LT and LTZ. Standard features included air conditioning, power windows and locks, a CD player, and cloth upholstery. LT models added features like chrome exterior trim, heated mirrors, and a premium sound system. LTZ models offered even more luxury, including leather upholstery, power-adjustable seats, and a navigation system. Optional extras included a sunroof, rear-seat entertainment system, and various towing packages. The interior design was functional and durable, prioritizing comfort and ease of use for long days on the road.
Chassis & Braking
The Sierra 3500HD featured a robust chassis designed to withstand heavy loads. 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 discs on all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) was standard. The heavy-duty suspension and braking system were crucial for safely managing the truck’s substantial weight and towing capacity.
Market Reception & Comparison
The 6.6L Duramax/Allison combination in the Sierra 3500HD was generally well-received by critics and consumers. It was praised for its powerful engine, smooth-shifting transmission, and comfortable ride. Fuel economy, while not exceptional, was respectable for a heavy-duty truck. Compared to the gasoline engine options, the diesel variant offered significantly more torque and towing capacity, making it the preferred choice for those needing to haul heavy loads. The Duramax/Allison combination was often compared favorably to the Cummins/automatic transmission pairings found in competing Ram and Ford trucks, with many considering it a top contender in the heavy-duty segment.
Legacy
The GMT900-generation Sierra 3500HD, particularly the 6.6L Duramax/Allison variant, has proven to be a durable and reliable truck. The LMM Duramax engine, while having some known issues with the fuel injectors, is generally considered a robust and long-lasting powerplant when properly maintained. Today, these trucks remain popular on the used car market, commanding relatively high prices due to their capability and reputation for reliability. They are often sought after by those needing a powerful and dependable truck for work or recreational purposes, and with proper maintenance, many continue to provide years of service.
