Ford Repair: 1984 F-250 line 6 4.9 liter manul 4 speed, tfi module, inner fender

Question
runs great until you drive for 5 miles plus then it cuts out, not like its running out of gas it doesnt bog down it just runs ruff on acceleration. it can run for half an hour and sill runs great until you drive it for about 5 miles  

Answer
Hello and thanks for the question...I'll try to help.
 Sounds like the ignition module (TFI module) and PIP (Profile Ignition Pickup) are going bad. OR, the Dura-Spark module is shot. The easy way to tell which is which is if you have a silver colored box on the left inner fender area --that's the Dura-Spark. If you have a gray module, with a wire harness connector plugged in to it at/on the distributor...........That's the TFI. The PIP is located inside the Dist.
I would replace them TFI & PIP --- OR the Dura Spark module.
Hope this helps,
Erik