The body change for 2003 3/4 and 1 tons WILL be that of the 2002 1500 series. The Cummins will be the diesel of choice, Dodge signed a contract with Cummins thru 2007. The Mercedes engine will be an option only on a heavier cab and chassis model that is supposed to be coming out. I did see a dually in mask here in the detroit area a couple of months ago. I could see thru the openings for the lights that the headlights and taillights looked identicle to the 2002 1500. I told a friend a DC that I saw the truck in mask, and told him about the engine leaking a large amount of oil. He asked if it was a Cummins or a Mercedes. I looked from underneath the truck (the engineer driving would not open the hood) and the engine looks the same as the current from the bottom. I told him that it was a 3500 4X4 4 door, and he said that it would then be a Cummins and not a Mercedes, as it is only coming in cab and chassis types. The interior also looked the same as the 2002 1500 on this truck. the engineer driving would only say that they are not trying to hide the fact that it is a Dodge, and obviously a 4X4 (Straight axle with quad link / coil spring front suspension) and a dually ( No hiding that). He said it was only still in mask because the 3500 series had not yet been officially released. There were no emblems on the doors.
My contact at DC works in the area to know all about the trucks and the diesels, and is very reliable... The new engine is supposed to be as quiet as the duramax (says no shutting down the engine at the Mc Donalds drive thru) and it in fact shares the same injectors and pump from bosch as the duramax.
Sorry so long, but I hope it clears up some questions...