The 2500 is a pig compared to the 1500. Just look underneith. The 2500 is much beefier and heavier. The 1500 HEMI might give you a run for your money, but you'd kill a 2500 HEMI. Really. They're pretty slow (fast for a truck, but slow for a car).
And ELMACHOGERACHO, stick to the Nissans and leave the trucks to those who don't drive Maximas.
The RAM Diesel for 2007 reportedly has a bigger 6.7L (up from 5.9L) engine, mostly to meet emissions, though (there is a power increase, too). It will be reportedly mated to a new Asian 7 speed auto rated for about 1000 lb-ft. of torque. (WOW) No Allison for the Dodge. Only Chevy/GMC will (err, do) have the Allsion 6-speed trans.