I was perusing wjjeeps.com and scanning the service bulletins and came across one that caught my eye. Factory Service Bulletin 09-003-03, 4.0 Multiple Cylinder Misfire. It has to do with engines that very seldom are run above 2500 rpm involving carbon deposits on the exhaust valves preventing them from spinning to clean themselves. The bulletin explains it all, but you can tell if this is the problem by removing the rocker arms and checking the wear pattern on the valve stems. If it's like a bullseye, it's spinning, but if it's straight lines across the stem, it's not. Carbon deposits can cause the valve to not close completely and cause a misfire. The bulletin explains how to correct this, but basically involves Sea Foam and a soak.