95 truck idles fine but stumbles badly while driving

Ive got a 95 chevy with a 350 tbi it starts and idles fine "but cold blooded" can rev it up some in park but when i go to drive it it stumbles and backfires through the intake ive replaced distributor,wires,plugs,cap,rotor and checked timing and fuel pressure and both are good when i get up to highway speed and you try to accelerate it sounds like its trying but it either doesnt or take forever to accelerate its got me stumped any ideas

Have you tried checking the IAC valve on the passenger side of the side of the throttle body? Mine did that and I replaced it and it ran fine after that. If you have a Chiltons or a Haynes manual for your truck it should tell you how to check it. If I remember it was only $30 or so dollars for a new one. And they a re super easy to change. Might want to also check you O2 sensor on the cat. how long has it been since you changed that. Are you seeing a drop in fuel mileage? Just a few things I can think of that might warrant checking out.