Stalls frequently

88 ford f250 with the 460 and manual trans. Dies intermittently. While driving under different throttle conditions, and even while parked and idling. Usually will restart after a few minutes, however I do not think it is an over-heat condition of some sensor, as somtimes it will fail to start when cold, only to be able to start up latter on. Fuel pressure check at a bit over 40 and does not loose pressure after turned off, volume appears good. Replaced tfi, stator, and fp and ecm relays.
When stalled and not restarting on its own, it try to run with starting fluid sprayed in. Also when stalled, and cranking engine, fuel pressure stays at over 40. Placing a test light across a fuel injector when its running gives a faint pulsing light as it should, but when stalled, while cranking the engine, no light at all.
also, new long block from ford put in last year, now has 15k miles. New clutch, harmonic balancer, plugs, wires. When it runs it runs great !