F250 dies when put in gear
 

I have an '89 f250 with 5.7L . it starts and idles fine but when you go to take off it wants to die, especially when it warms up. when your driving you can keep it running by keeping the rpm's up, but once you come to a stop and try to take back off it will die and then you have to hold the gas to the floor or pump the hell out of it then it'll start right back up. I've changed the filter, the throttle positioner,air control valve,and ran cleaner through it. was gonna change the filter in that black canister before the fuel pump but some ass took it out and didnt replace it, so i assume my injectors are screwed but thought i'd see if anyone has any sugestions before i pull out the injectors for a good cleaning? any help will be greatly appriciated!!