If the tires balance ok check for an out of round tire or a tire with a flat spot. I had that problem - tire balanced fine but have a vibration from around 55 to a little over 60. Once I found out what the problem was and changed the tires it has been a smooth ride.
Switch your tires front to back and see if it changes. As far as mileage goes, what speed is your engine turning at hiway speeds ? If it's loping along at 2,000 rpm it's going to suck gas. The 4.0 runs best at around 2400rpm. I know my XJ with LT235's at hiway speeds gets 16-18mpg in 5th gear at 60-65, in 4th gear at 65 it get 22, thats from leaving a scanner plugged in while driving and looking at it. At 75 in 5th it gets 22-24 depending on hills. This by the way is with the corrected speedometer gear and the chrysler scan tool.
If you have an auto tranny the correct speedometer gear is important.
I run 31 x 10.5 and I get the wobble to. I can usually give her some gas tho and it plains out. I have heard the same about the same side tire rotation fixing the problem. I would give that a go.
im still getting a vibration, and now that im on the high i would like to solve it if I can, Ive been told that might rear right tire bounces as a drive and my front end shakes side to side. What else could it be ??/