Well, I can tell you that the IDI will do better. Diesel is almost as much as Gas now, We have a Fullsize Dodge 15 pass. Van 5.9, 3.9 gears, 4 spd auto. My old man towed a loaded U-haul trailer to Manitoba, and figured the milage out to around 19 Mpg. (that was there and back not one way) The old '88 diesel we have supercab 1-ton dually 4:10 Limited slip, 2wd, C6 6.9 still runs every day for alot less then the van will and it gets about 15Mpg, go figure eh?