The 2500 and 3500 come with a 6.0L V8 engine standard, though a 6.6L turbo-diesel V8 is available. All Sierras come with a heavy-duty 6-speed automatic transmission. The 2500 and 3500 can be had as either a regular, extended or crew cab, with a standard or long bed, and with either a 2- or 4-wheel drivetrain. Dual rear wheels are available on some models. There are four trim levels, Work Truck, SLE, SLT and Denali. The 6.0L V8 engine is capable of 360 horsepower and 380 pound-feet of torque and the 6.6L turbo-diesel engine puts out 397 horsepower and 765 pound-feet of torque. When equipped with the diesel engine, the trucks are now capable of towing up to 10,000 lbs. The Sierra HD features a high-strength frame and heavy-duty front and rear suspension systems. Now rated at 6,000 pounds, all 4-wheel drive front suspension systems can easily support a snow plow when properly equipped. There are two suspension packages available for the 2500: the Z85 handling and trailering suspension and the Z71 off-road package, which adds high-performance shocks and a bigger stabilizer bar. Some standard features cross all Sierra lines, such as driver and passenger air bags, 4-wheel disc brakes with anti-lock brakes and tire pressure monitoring. GM's OnStar system is standard on the SLE trim and better. The system includes crash response, roadside assistance and remote door unlock services. The Sierra Denali brings the Sierra HD pickup's towing/hauling capabilities in a luxury and style-oriented package. The model's available in both 2500 and 3500 trim and both 2-wheel and 4-wheel drive--but only as a crew cab. The Denali comes with heavy-duty trailering gear, an electronic shift-on-the-fly transfer case on 4-wheel drive models, special wheels, body-color panels and molding and chrome trim, fog lights, power, heated mirrors, a high-performance Bose audio system and leather power-adjustable seats. Equipment availability is dependent on trim. Pretty much anything available in a pickup is available on a Sierra-- power everything, remote keyless entry, heated mirrors, privacy glass, bed liner, front tow hooks and chrome or aluminum wheels are all available across the lineup. Navigation is an option as is rear-seat entertainment for the crew cab models. Heated power seats are available, as is cruise control, sunroof and a rear window defogger. High-tech touches such as a rearview camera and rear parking assist are optional, too and would probably come in handy on a big truck like the Sierra. MP3-compatible stereo with XM satellite radio can be found on some models and a Bose system with USB interface is available.