Be careful with that skid plate and no external cooler for the trans. My buddy had an xj that he fried the transmission in because he had full skid plates and the radiator cooler just wasn't enough to keep the trans cool.
If you are overheating at highway speeds, you need to check your water pump. My little brother has a YJ (same motor) and going out to Glamis we overheated at anything above 60mph (4 people and full of gear). When we got home the radiator checked out, so we checked the WP and sure enough, the blades were eroded enough to not flow as much water under prolonged heavy load. Changed it at 195k miles, haven't had a problem since.
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