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 drivetrain. Dual rear wheels are available on some models. There are three trim levels: WT, LT and LTZ. The standard engine is a 6.0L V8 engine that is capable of 360 horsepower and 380 pound-feet of torque. A 6.6L turbo-diesel engine capable of 397 horsepower and 765 pound-feet of torque is also available. A fully-boxed chassis was introduced in 2011, which GM says is 125 times stronger than the unit it replaced and allows for a smoother ride as well as a much greater towing capacity. When equipped with the diesel engine, the trucks are now capable of towing up to 20,000 lbs. In addition to the stiff frame, heavy-duty front and rear suspension systems yield a 25% increase in 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 3-stage springs. Some standard features cross all Silverado 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 LT trim and better. It includes crash response, roadside assistance and remote door unlock services. 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. 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, 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 Silverado. MP3-compatible stereo with XM satellite radio can be found on some models and a Bose system with USB interface is available.