Well I guess I will add my two cents. I have owned a 2003 CTD 3/4 ton cc 48re. 3:73 had 137k on the clock when I traded for a 2012 CTD max tow 68re cc 4:10. Towed a 2004 36ft Cedar Creek with both trucks. Towed in the Smokes, Blue Ridge and front range of Rockies as well as flat. Mileage towing with either truck was to close to call. Both trucks were 4x4's. Got rid if 2012 and now I drive the truck in my sig. I only have a little over 4k on it so it isn't broken in yet. I have however towed in the flats and even up to the mountains in western Virginal pulling fiver in my sig. I have not hit the scales yet but it came out of the factory at 17235k so I weigh a little more then that. Truck runs fantastic. What impresses me the most besides the power and braking is how cool it runs. Def is a non issue, a lot of hype for nothing. The 2013's and above are also b20 comp.