The Heavy Duty Ram models are offered in three different cab styles--Regular Cab, Crew Cab and Mega Cab--as well as 6'-4" or 8' cargo box lengths. Crew Cab models are designed for occasional backseat use, while Mega Cab models have adult-size backseat accommodations--much like a full-size SUV. The 3500 can include a DRW (dual rear wheel) setup for heavy-duty towing and both versions may be either equipped with a 383-hp, 5.7-liter V8 or a 350-hp, 6.7-liter Cummins in-line six. The gasoline engine comes with a standard 5-speed manual, while the diesel offers a 6-speed manual or optional 6-speed automatic. The latter is actually the stronger option for towing, as it makes a mighty 881 pound-feet of torque at just 1500 rpm. The big diesel is also quite efficient while meeting 50-state emissions rules without using exhaust fluids, and it's the only diesel in this class to include an exhaust brake. With either engine, a part-time 4WD system (including low range) is available; with 4WD, the rack-and-pinion steering is replaced with a recirculating-ball system. Major trim levels for the Ram HD models include the SL, SLT, Laramie and Power Wagon. Each of these trims comes with the gasoline V8, and all but the Power Wagon can be optioned with the diesel. Compared to the light-duty Dodge Ram 1500 trucks, the heavy duty Ram 2500 and Ram 3500 trucks get a unique grille, hood and bumpers. Tow ratings range up to 17,600 pounds, with maximum payload of 5,130. A new integrated trailer brake control is now included in SLT, Outdoorsman, Power Wagon and Laramie models, and information from the system displays in the in-dash vehicle information center. The interior of the 2011 Ram 2500 and 3500 models can vary quite dramatically, with interior appointments spanning a wide range from a vinyl split bench in base SL models up to premium cloth benches or buckets in much of the lineup and premium leather in top Laramie models. The Ram HD models can be equipped with a number of features that haven't been offered in work-oriented HD models of the past. A heated steering wheel, heated rear seats, heated and ventilated front seats, memory seats, adjustable pedals, a navigation system and Sirius Backseat TV (children's programming) are all on offer. Other more work-oriented upgrades include larger mirrors and skid plates. Most of the safety features of personal light-duty trucks are also included in the Ram HD trucks, including side-curtain airbags, supplemental side airbags, and anti-lock brakes. A rear parking-assist system is available.