troubleshooting 1991 F-150?

1991 F-150

5.0 Liters

8 Cylinders

4WD

Details:

Truck had been sitting for 10 months, previously ran fine with no problems. Went to start the truck, engine sputtered and died, would not stay running. Could definitely hear misfiring/backfiring, Converter was running red hot and glowing when gas was applied to keep the engine on. Without gas, engine would stall out and die within 5-15 seconds.

Filled the truck up with new gas, added drygas, no difference. Discovered a loose spark plug wire, reattached it and the truck idled fine, purred like a kitten. Put the truck in drive, immediately the truck began running rough, misfiring (not nearly as badly as before) and sputtering. Truck was driveable but only just barely, was loud and jumpy, sputtery. Still, the truck idled fine when not in Drive.

I decided that perhaps I damaged the converter when troubleshooting the previous problem, and it was becoming clogged when the truck was moving, backing up the engine and causing problems. The exhaust was looking pretty hagard anyways and the muffler was rotted out, so I took the converter and everything behind it off the truck and put on a whole new system. This did not fix the problem, the truck still idled fine, but ran horribly in Drive. At this point, there was no O2 sensor on the truck, as the old was one stuck in the previous converter and would not come out. I got a new O2 sensor and put it in, started up the truck, and immediately it reverted back to the very first issue where it would not even stay running while idled. The truck misfires or backfires, sputters and dies, will not stay running. I disconnected the new O2 sensor to see if the problem would go away, and it didn't.

This is where I am at now. The truck has new plugs, ignition rotor and distributor cap look clean, whole new exhaust system, new gas, but still will not stay running and just sputters and dies while idling. I don't understand why the problem went away and then came back again.