sdmf420

I bought a 1993 jeep cherokee country 4.0 high output last year real cheap. it just had one problem.... it turns itself off hot or cold!. mostly hot. anyways im stumped... ive replaced fuel filter, radiator, pcm, ecu, coil, distributor, crank position sensor and more. a few other things.. it will start in overdrive, reverse, d3, 2and 1. neutral safety switch? it used to do it only after driving awhile, all of a sudden it would just shut off, no sputter, no indication it even turned off, stereo would stay on, lights etc.... just the rpms all of a sudden drop to 0 and its off. the way it runs is almost mint, engine sounds good, no shaking and you can barely hear it run! lots of power and good 4x4. this usually happens when im accelerating, but ive let it heat up in my driveway before and it has shut off. in winter sometimes i could make it far and sometimes id start up and move 20 feet and turn off, with a warm/ cold engine. but ALWAYS you have to turn key all the way off wait 5-10 seconds to start it or else it will just turn over without ignition. also if it defaults and you leave the key in the on position while its off, you can leave it for days, come back and try to start but it will not until key is turned all the way off, then on. help? p.s.. the jeep will drive around longer without default if im in 4x4 or part time. espesially 4 lo, seems to last much longer. im thinking possibly fuel pump but im tired of unloading money into it if i dont need to