Engine Performance problem
1989 Dodge Truck V8 Four Wheel Drive

I have a dodge d150 , 318 throttle body , 89 model , 4x4. It started cutting out, and u could hold it to the floor and gains no power. I replaced the coil , dist cap and butt , plugs and wires. It seemed to help for 3 or 4 days and started doing it again so i changed the fuel filter and pump , it ran fine for 40 mile then it was the same thing. I then thought may have gotten a bad pump so i changed it again. It ran fine a few miles now it is back to square one with the same problem. If anyone has any ideas i sure could use them.