Engine problems 97-4.0, need help diagnosing
I am having a problem with my 1997 Grand Cherokee that my mechanic can't diagnose. At highway speeds (65-75 mph) after driving for long periods of time (3 hours plus), the transmision (?) slips out of gear. It does not rev at all. I just lose power to the engine even when my foot is flat on the accelerator. Sometimes, after a few seconds it kicks right back in with a jolt, sometimes it just coasts on along and I need to pull over. After pulling over, I shut the engine, restart, and all is fine, but the problem recurrs after a few more miles. My mechanic can not reproduce this effect in the garage or on a test drive at highway speeds and can not diagnose the problem. I would appreciate any leads/help anyone can offer.