1988 7.5L F350 Superduty Problems

[jjkissers2002]

This is my father's truck. When we drive down the road it is almost as if the transmission disengages. The speedometer starts to fall and when you press on the gas it revs up but does not speed up. Sometimes this causes it to backfir as well. If we pull over and put the vehicle in park for a minuate then put it back in drive it will be fine for a little while and do the same thing. When this happens to the truck and we press on the gas to much while it is reving up it will stall out, just to start back up again in a minuate or two. He has recently had the fuel system worked on and did a full tune up.