Gearing is one way to go;several vendors offer a new ring and pinion set that's more acceptable for highway driving. I found that a set of LT 235/85R-16's will probably give you approx. 70 mph at about 3,200 rpm.That's not exactly the best speed for gas mileage,but it'll be better than stock. You can often pick up a set of four good used tires that size for 75.00 to 100.00,whereas the ring and pinion will cost you around 300.00,and at least 150.00 to have it installed. BTW-if you go for the tire size change do all four.Then you only need one spare,and changing just the rear ones will make your truck twitchy on the highway by reducing the rake of the kingpins.
You may also notice a little tire rub against the front springs when you turn it full lock,but it won't hurt anything.
