Mine is in the shop right now getting 4.56. It has the 4.0 / 5 speed. That is what was recomended to me. 4.88 for 35" tires. I'm not sure if the 4 banger will make a differance on gearing. MPG shouldn't be much worse. Better to just buy a new set of gears and be done. Mine was gutless in 5th and 4th wasn't much better, hope this cures it
1998 4.0 5 speed, Superior super 35 rear, Superior super 30 front, yukon air lockers x2. 3" Terra Flex suspension lift, 1.25" BL, 1" MML Engo 9K winch, Dick Cepeck Radial F-C 33/12.5/15.