NEW Dodge 2013 Ram 3500 4x4 -> ride is horrible! What to do?

The short wheel base is what's killing the ride. I have an '05 2500 that is the same as your truck and also "was" one of the worse riding trucks that I've ever owned. If you don't want to do what I did (factory suspension is gone) then I would get you about 300 lbs worth of sand bags and lay them directly between the rear fender wells. It will take the harshness out of it. Mine would literally get air under the rear tires on some overpasses.