I know a lot of folks love the 6.0 gas truck....i absolutely hated mine. It was a 2010 gmc 2500 4x4 with 3.73 gears. Pulling 8000 pounds i got 7-7.5 mpg on level ground in illinois and wisconsin and it rode like a battlewagon. Continually shifted up and down unless i locked it into fourth gear, which gave me less than 7 mpg.
After eight months, my wife refused to ride in it because it was awful. She wanted me to dump it on vacation in wisconsin. Got back to illinois and traded it the next week for my Ram hemi. Smoother ride, gets 9.5 to 10 mpg pulling the same trailer, not nearly the awful shifting, and more power on hills. Just a far better towing experience. If i had to go back to a GM truck with the 6.0, i would rather park the trailer pemanently. Just awful.
Certainly, i recommend that you test drive everything before you buy. I dont care for the Ram body style, but i dont see it from the inside,.....