Chevrolet's 2008 2500HD (three-quarter-ton) and 3500 HD (one-ton) are heavy-duty versions of the standard-duty Silverado pickup, all of which were completely redesigned for 2007. The HDs are available in three cab styles (regular, extended, and crew cab) and two box configurations (standard and long). Extended cab models come with smaller rear access doors that open 170 degrees and have fully opening windows. Crew cab models come with four full-size doors. 3500HD models come in two additional variants, identified by SRW (single rear wheels) or DRW (dual rear wheels, sometimes called Dually). The DRW models offer enhanced stability for those who routinely tow trailers near the upper end of capacity. Two suspensions are now offered on the HD trucks. The Z85 suspension is standard, and the optional Z71 suspension is oriented toward off-road duty and includes skid plates along with other additional equipment. Compared with the light-duty Silverado, the HD has a larger, bolder appearance, especially in front, with a wider grille, domed hood, and broader fenders. The HD trucks boast a ladder frame, a hydroformed front section, a structure designed for better crash protection, recirculating-ball steering gear aimed at improving steering feel, and a strong four-wheel disc brake system with anti-lock. The brakes also include an integrated trailer brake controller. Like the light-duty Silverado, the HD versions of the Silverado get two completely different interiors, depending on the intended use. The WT (Work Truck) and LT models, intended more for work use, come with a simplified instrument panel with large, functional controls, under-seat storage, and a cavernous double glove box. The luxurious LTZ, intended for those who might need to tow or haul in style, comes with an interior that rivals that of luxury SUVs, with a larger center console, heated leather bucket seats, and chrome trim. A 6.0L gasoline V8 engine with variable valve timing, making 353 horsepower and 373 lb-ft of torque, is standard on both models and a 6.6L Duramax diesel, making 365 hp and 660 lb-ft, is optional. Both engines are mated to six-speed automatic transmissions. Standout optional features on the LTZ include heated windshield washers, power-adjustable pedals, Ultrasonic Rear Parking Assist, a rear-seat DVD entertainment system on crew cabs, an EZ Lift tailgate, and a power-sliding rear window on extended and crew cabs. A wide range of audio systems includes MP3- and DVD-compatible players.