I had the exact same problem with my 1995 I-6. I replaced the fuel pump and nothing changed. Eventually the Jeep wouldn't start no matter how long I left the ignition on. I ordered a new computer and the Jeep fired right up, but then the problem persisted. The last thing I replaced was the fuel pump relay and I haven't had a problem since. If you have a fuel pressure gauge you might want to check the pressure when the problem happens.