The 2500 and 3500 come with a 6.0L V8 engine standard, though a 6.6L turbo-diesel V8 is available. All Silverados 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-drive configuration. Dual rear wheels are available on some models. There are three trim levels: WT, LT and LTZ as well as a special edition "High Country" model. The standard engine is a 6.0L V8 engine that is capable of 360 horsepower and 380 lb-feet of torque. It can also be ordered to run on compressed natural gas. A 6.6L turbo-diesel engine capable of 445 horsepower and 910 lb-feet of torque is also available. When equipped with the correctly, a 3500HD is capable of towing up to 23,000 lbs. In addition to the stiff frame, heavy-duty front and rear suspension systems provide incredible strength on 4-wheel-drive models. Now rated at 6,000 pounds, all 4-wheel drive front suspension systems can easily support a snow plow when properly equipped. The 2500 utilizes 2-stage leaf springs in the rear, while the 3500 makes use of three-stage springs. Some standard features cross all Silverado lines, such as driver and passenger air bags, 4-wheel disc anti-lock brakes and tire pressure monitoring. GM's OnStar system is standard on the LT trim and better. Like most GM vehicles on which it's equipped, OnStar offers crash response, roadside assistance and remote door unlock services. There are two suspension packages available for the 2500: the standard Z85 handling and trailering suspension and the Z71 off-road package, which adds high-performance shocks and a bigger stabilizer bar. Equipment availability is dependent on trim. Pretty much anything available in a pickup is available on a Silverado -- power everything, remote keyless entry, heated mirrors, privacy glass, bed liner, front tow hooks and chrome or aluminum wheels. Navigation is available, as is rear-seat entertainment for the crew cab models. Heated power seats are available, along with cruise control, sunroof and a rear window defogger. High-tech touches such as a rearview camera and rear parking assist are available as well. An MP3-compatible stereo with XM satellite radio is standard on many models. A high-performance Bose system with USB interface is available.