I am running a 1997 3500 ext cab . Converted from 10 cylinder gas to a 96 12 Valve cummins with a 6 speed stick big conversion . It is a 4x4 makes it a bit higher 235/85/26 Hankook mileage 20 mpg 68 mph 1900 rpm . Did a frame off cab sound proofed all new drive parts Got a lot stuck in original injection pump and lift pump . Maybe that was the only thing did wrong ? Have 30000 on truck since build . Thought it was ready for the trip , guess not . I wil get it fixed , Let you know . Have a great new year every body .Pete