The GMC Sierra 2500HD III, specifically the Extended Cab Long Box configuration with the 6.0L V8 engine paired to an automatic transmission and capable of running on Compressed Natural Gas (CNG), was produced for a limited run between 2013 and 2014. This variant represented a niche offering within the GMT900 platform – a heavy-duty pickup truck designed for demanding work and towing applications. It aimed to provide a balance between capability, alternative fuel options, and the convenience of an automatic transmission, appealing to fleet operators and individual buyers seeking a robust and versatile vehicle.
Technical Specifications
| Brand | GMC |
| Model | Sierra 2500HD |
| Generation | Sierra 2500HD III (GMT900, facelift 2011) Extended Cab Long Box |
| Type (Engine) | 6.0 V8 (301 Hp) Automatic CNG |
| Start of production | 2013 |
| End of production | 2014 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Pick-up |
| Seats | 5 |
| Doors | 2 |
| Fuel Type | Petrol / CNG |
| Power | 301 Hp @ 5000 rpm |
| Power per litre | 50.4 Hp/l |
| Torque | 452 Nm @ 4200 rpm / 333.38 lb.-ft. @ 4200 rpm |
| Maximum engine speed | 6000 rpm |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | Vortec LC8 |
| 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, VVT |
| 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 |
| Fuel tank capacity | 136 l / 35.93 US gal | 29.92 UK gal |
| CNG cylinder capacity | 67 kg |
| Length | 6337 mm / 249.49 in. |
| Width including mirrors | 2032 mm / 80 in. |
| Height | 1971 mm / 77.6 in. |
| Wheelbase | 4018 mm / 158.19 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) | 15.8 m / 51.84 ft. |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives the rear wheels of the vehicle. |
| Drive wheel | Rear wheel drive |
| Number of gears and type of gearbox | 6 gears, automatic transmission Hydra-Matic |
| Front suspension | Coil spring, Double wishbone, Transverse stabilizer |
| Rear suspension | Rigid axle suspension, Leaf spring |
| Front brakes | Ventilated discs, 350×40 mm |
| Rear brakes | Ventilated discs, 360×34 mm |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Cone worm with recirculation balls |
| Tires size | 245/75 R17; 265/70 R17; 265/70 R18; 265/60 R20 |
| Wheel rims size | 7.5J x 17; 8J x 18; 8.5J x 20 |
Powertrain & Engine Architecture
At the heart of this Sierra 2500HD variant lies the Vortec LC8 engine, a 6.0-liter (364 cubic inch) V8. This engine is a member of the Vortec family, known for its robust construction and relatively simple design. The LC8 utilizes a cast iron block and aluminum cylinder heads, featuring a 9.6:1 compression ratio and two valves per cylinder operated by an overhead valve (OHV) valvetrain. Variable Valve Timing (VVT) was incorporated to improve efficiency and low-end torque. Fuel delivery is managed by a multi-port fuel injection system. The engine was designed to run on gasoline, but this specific model was factory-equipped to also operate on Compressed Natural Gas (CNG), requiring a dedicated CNG fuel tank and fuel delivery system alongside the standard gasoline tank. The Hydra-Matic 6L80E six-speed automatic transmission was the sole transmission option, chosen for its durability and ability to handle the engine’s torque output.
Driving Characteristics
The combination of the 301 horsepower Vortec LC8 and the six-speed automatic transmission resulted in a truck that prioritized usability and towing capacity over outright speed. While not as quick as versions equipped with the more powerful 6.6L Duramax diesel engine, the 6.0L V8 provided ample power for everyday driving and hauling moderate loads. The automatic transmission offered smooth shifts and convenient operation, particularly in stop-and-go traffic. The gear ratios were optimized for towing, providing strong low-end torque. However, this came at the expense of fuel economy, especially when operating in gasoline mode. The CNG capability offered a potential cost savings on fuel, but CNG refueling infrastructure was, and remains, limited in many areas.
Equipment & Trim Levels
The 2500HD Extended Cab Long Box with the 6.0L V8 and CNG option typically fell into a mid-range trim level, often designated as the SLE or SLT. Standard features included air conditioning, power windows and locks, a basic audio system, and vinyl upholstery. The Extended Cab provided additional interior space compared to the regular cab models, offering limited seating for rear passengers. Optional extras included leather upholstery, a premium audio system, navigation, and various towing packages. The CNG system itself was a significant factory option, adding a dedicated fuel tank and associated components.
Chassis & Braking
The Sierra 2500HD’s chassis was built for heavy-duty use. It featured a fully boxed frame and a robust suspension system. The front suspension utilized coil springs and a double wishbone design with a transverse stabilizer bar. The rear suspension employed a traditional leaf spring setup, designed to handle heavy payloads. Braking duties were handled by ventilated disc brakes on all four wheels, with ABS (Anti-lock Braking System) as standard equipment. The rear brakes were slightly smaller in diameter than the front brakes. Steering was accomplished via a cone worm with recirculation balls system.
Market Reception & Comparison
The 6.0L V8/Automatic CNG Sierra 2500HD was a relatively uncommon configuration. Critics generally praised the engine’s reliability and adequate power, but noted its lower fuel economy compared to the diesel options. The CNG capability was seen as a positive for environmentally conscious buyers and those with access to affordable CNG fuel. Compared to the 6.6L Duramax diesel, the 6.0L V8 offered significantly less torque and towing capacity, but at a lower initial cost. Compared to the 6.0L V8 in standard gasoline configuration, the CNG variant offered the potential for lower fuel costs, but required access to CNG refueling stations.
Legacy
The 6.0L Vortec LC8 engine, in general, has a reputation for being a durable and reliable powerplant, though it is known to have potential issues with oil consumption as it ages. The Hydra-Matic 6L80E transmission is also considered a robust unit. The CNG-specific components, however, may require specialized maintenance and repair. Today, these trucks are found primarily in the used market, often with significant mileage. Their value is typically lower than comparable diesel-powered models, but they can represent a good value for buyers seeking a capable and affordable heavy-duty pickup. The limited production numbers and unique CNG configuration may make these trucks appealing to collectors and enthusiasts.
