I have the truck you are talking about exactly. I love it but I came form a 2000 1500 gasser, and never have never owned a diesel. My TT is a bit smaller at only 6700 on the scale and I hardly know it is behind me. I have only towed 2 times with the truck as I have only had it since September. But one of those two trips was a 350 long trip. Got in the truck set the cruise at 62 and let her go. YOu are pretty correct on the MPG's as to what I am getting here, although you may see a little better since you are at sea level and I live at 4700 ft. I am using this truck as the DD until my wife gets a new car in a year or so and enjoy driving it every day, and can not imagine having anything else.
That being said it is up to you on what makes you happy. If you were out here in the wet and climbing the Sierra's and the Rocky's, Dmax, Cummins or Powerstroke would probably be your best option. Several have switched and been very happy, and several have not. Look up some of IB516's reviews on his 6.4 Hemi. Not the exact truck but close.
Good luck.
