This doesn't answer your whole question, but remember the front end of the Dodge 2500 is beefed up to handle the weight of the Cummins. My 5.9l weighs around 1175lbs. Something to consider.
I own a 5.9L Cummins, and love it! The Cummins is a straight-six which means it inherantly has more torque, it also has 30% fewer moving parts than a V-8 diesel. Besides all that good stuff, Cummins makes rugged engines.