The GMC Sierra 3500HD III, produced from 2007 to 2010, represented a significant evolution in GMC’s heavy-duty truck lineup. This generation, designated GMT900, offered a blend of increased capability, refined comfort, and advanced technology for the demanding needs of truck users. The Extended 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, was a popular choice for those requiring substantial towing and hauling capacity. This particular variant occupied a sweet spot in the Sierra 3500HD range, offering a powerful and capable workhorse without the premium price tag of higher trim levels.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD III (GMT900) Extended Cab Long Box |
| Type (Engine) | 6.6 Duramax TD V8 (365 Hp) 4WD DRW Automatic |
| Start of production | 2007 |
| End of production | 2010 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.9 kg/Hp, 112 Hp/tonne |
| Weight-to-torque ratio | 3.6 kg/Nm, 274.7 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 | 3258 kg, 7182.66 lbs. |
| Max. weight | 5171 kg, 11400.1 lbs. |
| Max load | 1913 kg, 4217.44 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 | 6330 mm, 249.21 in. |
| Width including mirrors | 2436 mm, 95.91 in. |
| Height | 1927 mm, 75.87 in. |
| Wheelbase | 4001 mm, 157.52 in. |
| Front track | 1742 mm, 68.58 in. |
| Rear (Back) track | 1897 mm, 74.69 in. |
| Ride height (ground clearance) | 233 mm, 9.17 in. |
| 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 |
INTRODUCTION
The GMC Sierra 3500HD III, specifically the Extended Cab Long Box configuration with the 6.6L Duramax diesel and Allison automatic, was a work-focused truck designed for serious hauling and towing. Introduced in 2007, this iteration of the Sierra 3500HD built upon the foundation of the GMT900 platform, offering improvements in interior refinement, ride quality, and powertrain efficiency compared to its predecessors. The “DRW” designation indicates a Dual Rear Wheel configuration, further enhancing stability and payload capacity. This model year represented a transitional period for GMC, moving towards a more premium feel while maintaining its reputation for rugged dependability. It was positioned as a step up from the lighter-duty Sierra 2500HD, and below the more luxurious Denali trim levels.
Powertrain & Engine Architecture
The heart of this Sierra 3500HD is the Duramax LMM 6.6-liter V8 turbodiesel engine. This engine, a product of a joint venture between General Motors and Isuzu, is a robust and reliable powerplant. The LMM featured a redesigned combustion chamber and improved fuel injection system compared to earlier Duramax engines, resulting in increased power and reduced emissions. The engine utilizes a common-rail direct injection system, delivering fuel at extremely high pressures for optimal combustion. The valvetrain employs two valves per cylinder, operated by a pushrod (OHV) design, a configuration favored for its simplicity and durability. The Allison 1000 six-speed automatic transmission is a crucial component, specifically engineered to handle the immense torque output of the Duramax engine. This transmission is known for its durability and smooth shifting characteristics, and features a lock-up torque converter for improved fuel efficiency. The turbocharger and intercooler work in tandem to increase air density, boosting power and reducing exhaust emissions.
Driving Characteristics
The 365 horsepower and 895 lb-ft of torque delivered by the Duramax/Allison combination translate into impressive real-world performance. While not a sports truck, the Sierra 3500HD offers ample power for accelerating with a load or tackling steep grades. The Allison transmission’s six gears allow the engine to operate efficiently at highway speeds, contributing to reasonable fuel economy for a heavy-duty truck. Compared to the gasoline-powered versions of the Sierra 3500HD, the diesel offers significantly more torque at lower RPMs, making it ideal for towing. Compared to higher-output Duramax variants available in later years, this 365hp version provides a balance between power and fuel efficiency. The DRW configuration enhances stability, particularly when towing heavy loads, but can make maneuvering in tight spaces more challenging.
Equipment & Trim Levels
The Extended Cab configuration provided additional passenger space compared to the standard cab models, offering a small rear seat suitable for occasional use. Standard features typically included air conditioning, power windows and locks, and a basic audio system. The interior materials were durable and functional, reflecting the truck’s work-oriented nature. Optional extras included leather upholstery, a premium audio system, navigation, and various towing packages. The specific trim level (e.g., SLE, SLT) determined the level of standard equipment and available options. The Long Box provided a substantial cargo bed, ideal for hauling large items.
Chassis & Braking
The Sierra 3500HD’s chassis is built for heavy-duty use, featuring a robust frame and heavy-duty suspension components. The front suspension utilizes an independent torsion bar setup with double wishbones, providing a comfortable ride while maintaining stability. The rear suspension employs a traditional leaf spring design, capable of handling substantial loads. Braking duties are handled by ventilated disc brakes on all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) is standard, enhancing safety during emergency braking situations. The DRW configuration utilizes larger brakes to cope with the increased weight and stopping demands.
Market Reception & Comparison
The 2007-2010 GMC Sierra 3500HD with the Duramax/Allison powertrain was generally well-received by critics and truck buyers alike. It was praised for its powerful engine, smooth transmission, and impressive towing capacity. Fuel economy, while not exceptional, was considered reasonable for a truck of its size and capability. Compared to the Ford Super Duty and Ram Heavy Duty trucks of the same era, the Sierra 3500HD offered a competitive combination of features, performance, and reliability. The Duramax engine, in particular, earned a reputation for longevity and dependability.
Legacy
The Duramax LMM engine and Allison transmission combination found in this Sierra 3500HD have proven to be remarkably durable. Well-maintained examples continue to provide reliable service today. The GMT900 platform, while superseded by newer generations, remains a popular choice for those seeking a capable and affordable heavy-duty truck. On the used car market, these trucks command reasonable prices, reflecting their age and mileage, but also their proven track record. Common maintenance items include regular oil changes, fuel filter replacements, and occasional repairs to the cooling system. The DRW configuration, while offering increased capability, can result in higher tire costs and potentially more complex maintenance procedures.
