The GMC Sierra 3500HD III, produced from 2007 to 2010, represented the third generation of GMC’s heavy-duty full-size pickup truck. This iteration, designated GMT900, was a significant update to the previous generation, focusing on increased capability, improved refinement, and a more modern interior. The Extended Cab Long Box configuration, paired with the 6.0-liter Vortec V8 engine producing 360 horsepower and a four-wheel-drive Dual Rear Wheel (DRW) setup with an automatic transmission, was a popular choice for those needing substantial towing and hauling capacity. This particular variant occupied a sweet spot in the lineup, offering a balance between capability and everyday usability, appealing to both commercial users and private owners requiring serious truck performance.
Technical Specifications
| Brand | GMC |
| Model | Sierra 3500HD |
| Generation | Sierra 3500HD III (GMT900) Extended Cab Long Box |
| Type (Engine) | 6.0 V8 (360 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 | Petrol (Gasoline) |
| Weight-to-power ratio | 8.2 kg/Hp, 121.7 Hp/tonne |
| Weight-to-torque ratio | 5.7 kg/Nm, 174.1 Nm/tonne |
| Power | 360 Hp @ 5400 rpm |
| Power per litre | 60.3 Hp/l |
| Torque | 515 Nm @ 4200 rpm, 379.84 lb.-ft. @ 4200 rpm |
| Maximum engine speed | 6000 rpm |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Vortec LY6 |
| Engine displacement | 5967 cm3, 364.13 cu. in. |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 101.6 mm, 4 in. |
| Piston Stroke | 92 mm, 3.62 in. |
| Compression ratio | 9.6:1 |
| Number of valves per cylinder | 2 |
| Fuel injection system | Multi-port manifold injection |
| Engine aspiration | Naturally aspirated engine |
| Valvetrain | OHV |
| Engine oil capacity | 5.7 l, 6.02 US qt | 5.02 UK qt |
| Coolant | 15.5 l, 16.38 US qt | 13.64 UK qt |
| Kerb Weight | 2958 kg, 6521.27 lbs. |
| Max. weight | 5171 kg, 11400.1 lbs. |
| Max load | 2213 kg, 4878.83 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%) | 5307 kg, 11699.93 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 Hydra-Matic |
| 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 6.0-liter V8 and automatic transmission, was a workhorse designed for demanding tasks. Introduced in 2007, this model year marked a significant overhaul of GMC’s heavy-duty lineup. Built on the GMT900 platform, it offered increased payload and towing capacities compared to its predecessors. The “HD” designation signified “Heavy Duty,” emphasizing its capability. The Extended Cab provided additional interior space, making it more practical for crews or passengers, while the Long Box offered ample cargo-carrying capacity. The 4WD DRW (Dual Rear Wheel) configuration further enhanced stability and load-handling capabilities, making it a popular choice for commercial applications like construction, farming, and hauling heavy equipment.
Powertrain & Engine Architecture
At the heart of this Sierra 3500HD was the Vortec LY6 6.0-liter V8 engine. This engine, a member of GM’s Vortec family, was known for its robust construction and reliable performance. It featured a cast iron block and aluminum cylinder heads, contributing to its durability. The LY6 utilized a multi-port fuel injection system, delivering fuel directly to each cylinder for efficient combustion. The engine employed an overhead valve (OHV) valvetrain, a traditional design favored for its simplicity and reliability. The 6L80E six-speed automatic transmission, a Hydra-Matic unit, was standard. This transmission offered smoother shifting and improved fuel economy compared to older four-speed automatics. The 6L80E was electronically controlled, adapting to driving conditions for optimal performance. The combination of the 6.0L V8 and the 6L80E transmission provided a good balance of power and drivability, making it suitable for both work and occasional personal use.
Driving Characteristics
The 6.0-liter V8, producing 360 horsepower and 380 lb-ft of torque, provided ample power for towing and hauling. However, it wasn’t designed for outright speed. Acceleration was adequate, but the truck’s substantial weight (around 6,500 lbs) limited its responsiveness. The six-speed automatic transmission helped to keep the engine in its optimal power band, providing reasonable acceleration in most situations. The DRW configuration significantly improved stability, especially when towing heavy loads. The rear suspension, utilizing leaf springs, was tuned for load-carrying capacity rather than ride comfort. While the ride could be firm when unloaded, it smoothed out considerably when a load was added. The 4WD system provided excellent traction in various conditions, making it capable off-road as well.
Equipment & Trim Levels
The Sierra 3500HD offered a range of trim levels, with the base model providing essential features and higher trims adding more luxury and convenience items. Standard equipment on the 6.0L automatic models typically included air conditioning, power windows and locks, and a basic audio system. The Extended Cab configuration offered a split bench seat in the rear, providing seating for three additional passengers. Optional extras included leather upholstery, a premium audio system, navigation, and a power sunroof. The interior design was functional and durable, with a focus on practicality rather than lavishness. The dashboard layout was straightforward, with easy-to-read gauges and intuitive controls.
Chassis & Braking
The GMT900 chassis was a fully boxed frame, providing a solid foundation for the heavy-duty truck. The front suspension utilized an independent torsion bar setup with double wishbone components, offering a reasonable level of ride comfort and handling. The rear suspension employed a traditional leaf spring design, optimized for load-carrying capacity. 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 configuration provided increased braking capacity and stability, particularly when hauling heavy loads.
Market Reception & Comparison
The GMC Sierra 3500HD III was generally well-received by critics and consumers alike. It was praised for its increased capability, improved refinement, and robust powertrain. Compared to its competitors, such as the Ford Super Duty and Ram Heavy Duty, the Sierra 3500HD offered a competitive combination of features and performance. The 6.0-liter V8 engine was considered a reliable and capable powerplant, although some critics noted that it lacked the outright power of the diesel options available in the lineup. Fuel economy was typical for a heavy-duty truck, averaging around 12-15 mpg in real-world driving. The DRW configuration, while offering increased stability and load capacity, did come with a higher price tag and reduced maneuverability.
Legacy
The GMC Sierra 3500HD III, particularly the 6.0-liter V8/automatic combination, has proven to be a durable and reliable truck. The Vortec LY6 engine is known for its longevity, and the 6L80E transmission has also demonstrated good reliability. In the used car market, these trucks remain popular among those needing a capable and affordable work truck. While maintenance costs can be higher than those of lighter-duty trucks, the Sierra 3500HD’s robust construction and readily available parts supply make it a relatively easy vehicle to maintain. The GMT900 generation Sierra 3500HD represents a significant step forward in heavy-duty truck design, offering a blend of capability, refinement, and reliability that continues to appeal to buyers today.
