Confirming rumors on Internet enthusiast sites and the suspicions of trade-press writers, Dodge Truck officials said they are preparing higher gross-weight versions of the diesel-powered Ram conventional for sale later this year.

Medium-duty Ram 4500 and 5500 models will cover Classes 4 and 5, which can only add more heat to an already competitive market segment.

At an embargoed briefing at Chrysler Group's Auburn Hills, Mich., headquarters late last year, executives told reporters they would announce the heavier Rams at the Chicago Auto Show this month. They also plan to show off redesigned and restyled Sprinter vans at the Toronto show about a week later. The new Sprinters, which will be sold as Dodges and Freightliners, were unveiled last year in Europe.

The midrange Rams, using cabs from the 1500, 2500 and 3500 series pickups and frame designs from the more recent Ram 3500 Heavy Duty, will be sold only as Cab Chassis vehicles for the mounting of a variety of commercial bodies. They'll come only with the 6.7-liter Dodge-Cummins Turbo Diesel, rated at 305 horsepower and 610 pounds-feet, with six-speed manual or six-speed automatic transmissions. They'll be available with two-door Regular or four-door Quad Cabs and with two- or four-wheel drive.

Ram 4500 Heavy Duty will be rated at 16,500 pounds gross vehicle weight and the Ram 5500 HD at 19,500 pounds. Their frames consist of new front sections and upgraded C-channel main-rails spaced 34 inches apart in the rear, with bolted crossmembers. They'll also have higher-rated suspensions, brakes, wheels and tires, giving them a slightly higher stance than the Class 3 Ram 3500 HD on which they are based. Production of the 4500 and 5500 HDs will commence in July at a DaimlerChrysler plant in Mexico, where 3500 HDs are now built.

The gasoline Hemi V-8 will not be offered in the Ram 4500 and 5500 HDs, executives said, because more than 85 percent of customers for Class 2 and 3 pickups and cab-chassis models pick the diesel.

Conversely, the new Sprinter vans will get a new gasoline V-6 option in addition to the current five-cylinder Mercedes-Benz turbodiesel, which will continue.

The Class 4 and 5 commercial truck market now sees sales of about 140,000 units a year, Dodge execs said, and is expected to grow about 20 percent by 2015. Ford and General Motors now grab most sales in the conventional-cab segment, though International also offers conventional and low cab-forward models and Hino has conventionals. Both Ford and GM also sell LCFs, as do Isuzu, Mitsubishi Fuso and Nissan UD. Competition will be based on features and price, and most contenders are expected to try to fiercely defend their current market shares.