If the XJ is in a good/reasonable state of repair you should not have no problems. In the past I have driven from Dallas,TX to Waterbury CT and from Miami FL to DesMoines, IA with never a mishap. I never pulled a trailor so that may load the 4.0L and the AW4 a bit more. However, at that time I had 30" tires and 3.55 gears. I have been using 15-50 Amsoil since 2004 and change it between 12,000 and 14,000 miles. I second the oil cooler for the AW4.