I do have 4wd,truck has 40,000 miles auto,stock tires I see 17 highway @60-65 I see 19~20 if I keep it at 58 mph unloaded to be sure and no topper I have a slide in Lance and I see 12~14 with that. I hauled a giant Dresser bulldozer (dont know the weight) I saw 12 mpg, then hauled a smaller Komauo ? Bulldozer and saw 14. I would love to have my 3:54 s back. I may ... . may go for a overdrive unit,I know the payback will take more than one life time to be cost effective but I just like lower RPMs.