Just put a new fuel pressure regulator in her yesterday and it didn't solve the problem. She still runs great on COLD START and only until the truck reaches normal running temp. Then it runs like crap, skipping, and missing. It seems better with the O2 sensor off but still like crap. I have an O2 sensor waiting at Sanels, as well as a thermo sensor but at which point do I stop buying all these sensors? I could literally spend hundreds of dollars replacing one at a time.

I know this is an old truck and hard to diagnose but here's a list of what's already been done.

compression test
leakdown test
vacuum test
heat test
valve adjustment
exhaust gas analyzer
fuel pressure test
replaced the fuel pressure regulator
disconnected the O2 sensor (got better/lower O2 readings on exhaust gas analyser by doing this)
fuel injector cleaner using fuel pressure guage kit