I have an 81 CJ7 with a 5 speed transmition I6-258 and 35" tires. Currently I am limited to top end speed in 3rd gear at 65mph. 4th and 5th gear do not seem to increase speed, just lower RPMs. I am looking to change the gear ratio so I can cruze comfortably at 75 on the high way and still keep my offroad torque. Any sugestions on what gears I should go with or action I should take to correct this situation?