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 robust platform designed for demanding work and towing applications. Within this generation, the Regular Cab Long Box configuration equipped with the 6.6-liter Duramax Turbo Diesel V8 engine producing 365 horsepower and paired with a 4WD Dual Rear Wheel (DRW) automatic transmission, stood as a particularly capable and popular choice for commercial users and those requiring substantial hauling capacity. This variant occupied a premium position within the 3500HD range, offering a balance of power, durability, and functionality.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD III (GMT900) Regular 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 | 2 |
| Doors | 2 |
| Fuel Type | Diesel |
| Weight-to-power ratio | 8.4 kg/Hp, 119.2 Hp/tonne |
| Weight-to-torque ratio | 3.4 kg/Nm, 292.3 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 | 3062 kg (6750.55 lbs.) |
| Max. weight | 5171 kg (11400.1 lbs.) |
| Max load | 2109 kg (4649.55 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 | 5714 mm (224.96 in.) |
| Width including mirrors | 2436 mm (95.91 in.) |
| Height | 1919 mm (75.55 in.) |
| Wheelbase | 3378 mm (132.99 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.) |
| Drivetrain Architecture | All wheel drive (4×4). ICE drives rear wheels, front wheels engaged via clutch. |
| 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 turbocharged diesel V8. 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’s valvetrain employed an overhead valve (OHV) configuration, known for its simplicity and durability. The turbocharger, coupled with an intercooler, provided increased air intake, boosting power and torque output. The Allison 1000 six-speed automatic transmission was specifically designed to handle the substantial torque produced by the Duramax engine. This transmission featured a lock-up torque converter for improved fuel efficiency at highway speeds and provided smooth, reliable shifting even under heavy loads.
Driving Characteristics
The 365 horsepower and 895 lb-ft of torque delivered by the Duramax engine and Allison transmission combination resulted in impressive performance, even with the substantial weight of the truck. While not designed for outright speed, this variant excelled in towing and hauling. The Allison transmission’s gear ratios were optimized for pulling power, providing strong acceleration from a standstill and maintaining momentum on inclines. Compared to the gasoline-powered versions of the Sierra 3500HD, the Duramax diesel offered significantly more torque at lower RPMs, making it ideal for demanding tasks. The Dual Rear Wheel configuration enhanced stability when towing heavy loads, and the 4WD system provided excellent traction in various conditions. The ride quality, while firm due to the heavy-duty suspension, was acceptable for a truck of this class.
Equipment & Trim Levels
The Sierra 3500HD in this configuration typically came standard with features geared towards work and utility. This included a heavy-duty vinyl interior, air conditioning, and a basic audio system. Optional extras included power windows and locks, upgraded audio systems, leather upholstery, and a navigation system. The Regular Cab configuration prioritized functionality over luxury, offering a spacious work environment for the driver and passenger. The long box provided ample cargo space for tools and equipment. Trim levels varied, but this powertrain was often found in the WT (Work Truck) and LT trims, offering a balance of affordability and features.
Chassis & Braking
The GMT900 chassis was built for durability and strength. 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, capable of supporting heavy loads. Braking duties were handled by ventilated disc brakes on all four wheels, providing ample stopping power. An Anti-lock Braking System (ABS) was standard, enhancing safety during emergency braking situations. The DRW setup significantly increased the truck’s stability and load-carrying capacity.
Market Reception & Comparison
The GMC Sierra 3500HD with the Duramax diesel and Allison automatic was widely praised by critics and consumers alike. It was consistently ranked among the top heavy-duty trucks in its class, lauded for its power, reliability, and towing capabilities. Compared to the gasoline-powered Sierra 3500HD models, the diesel variant offered superior fuel economy when towing and hauling, despite its higher initial cost. The Duramax/Allison combination was often preferred over competing diesel engines and transmissions from Ford and Ram due to its reputation for longevity and smooth operation.
Legacy
The Duramax LMM engine and Allison 1000 transmission have proven to be exceptionally durable powertrains. Well-maintained examples of the 2007-2010 Sierra 3500HD continue to be highly sought after in the used truck market. These trucks are known for their ability to accumulate high mileage while remaining reliable. Common maintenance items include regular oil changes, fuel filter replacements, and occasional repairs to the cooling system. The LMM Duramax is generally considered to be a robust and relatively trouble-free engine, making it a popular choice for those seeking a capable and long-lasting heavy-duty truck.
