1988 Chevy 1500. 350 motor 2 wheel drive

[Just Bill]

Truck was running rough at 50 mph. Would run good higher/lower speeds. Next day got worse. Died at intersection. Wouldn't start. Backfired and loud noise under hood. 10-15 minutes later started ran rough died again. Looked at distributor and cap was broken at center prong. Replaced cap rotor. Started and idled good. Out in gear and died. Replaced egr, air intake valve, fuel and air filters. Injectors are putting out good cone. Truck sounds great at idle. Out wants to stall in gear. Played with gas pedal and will run but a lot of hesitation then dies at stop in gear.

Suggestions on what to do next? I am just a normal maintenance type mechanic.

Thanks

[silveradosid]

fuel pressure regulator

[jofrye56]

Check distributor 

I've replaced mine twice

bushings wear out