If you can get a model year 2012 rig you could get the 6 speed Torqshift.(I think) The final drive ratio is a bit lower with the torqshift at .674 compared to .71 for the 4R100. I have a econoline with the 4R100 and the mileage is bad,but I do much better with the 6 speed. You eat up more in gas with the older transmission, 5 speed probably in the middle I suppose. It's not just the final ratio's that's important, but the rig can be in a much more appropriate gear going up those gas sucking mountains.