If u assume u can get diesel for the same amount as gas, and tow the vehicle exclusively, its a little over 4 cent a mile with a 90,000 mile payback. If your like me, 12 cents higher for diesel in my town and don't tow too much it can be 2 cent per mile with payback at 188,000 miles. I've got only got a little over 46,000 miles on mine and had it since June 1998. I know what the right decision was for me.