Idle problems and stumbling/backfiring at speed

[DouglasU]

I don't know if these are related but I have an 88 150 witha 4.9l/5-speed. The engine idles at 1200-1500rpm and also has a miss at idle. When running at highway speed it will often (but not always) start to miss, backfire, and stumble which usually will go away if you floor it, it often comes back
minutes later. This truck was acting like this until one day it wouldn't run at all which is when I bought it and traced out and replaced a faulty crankshaft position sensor which I think is unrelated. The computer will not give me any code but the 10 code. The ignition module tests good, the coil resistence test is good, the fuel pressure at the fuel rail is good at idle, it has new plugs, cap/rotor, and filters. The timing is set correctly. If anyone can point me in the right direction or has had a similar problem I would appreciate your input.