cherokee keeps shutting down

92 XJ, 4LHO, 270K (60K on motor), started experiencing stutter-step in idle and planned on tune up. All of a sudden, from cold just as temp starts to rise, no hesitation, no rough idle, just shuts down and won't restart til cold. I did plugs, wires, cap, rotor, fuel filter this AM. Started and ran fine right up to temp and through a 10-15 minute test drive. Left alone for awhile, maybe 2 hours, started OK, but back to shutdown as temp starts rising. Although, this time it restarts and will run OK and shut off/on with ignition as long as temp doesn't get to cold?????????? Help.