89 Camaro LB9 5 sp. no mods-power loss

Engine loses power after warm up no codes set no high temp and no knocking.  Power loss so severe that unable to use 3,4 or 5th gear.  Eventual stall and hard restart. only complete cool down restores power.  Any clues?  

Would you say the power loss comes once the computer goes into closed loop? If so that is when your O2 comes into play and is adjusting your fuel trim. Maybe try unplugging the O2 and see how it goes. Maybe your cat could be plugged? look at it and see if it looks dark and burned on the engine end of it. Also see if it glows red when the power loss and stall happens.  

1st time car was at interstate speeds and running for 45 minutes but was also very heavy rain so the cat issue was not readily visible.  car was towed.  More recent problems have shown up at much shorter time from start-cat is a definite possibility.  Also all plugs are showing signs of oil fouling-could this contribute to a cat problem?  

Yes oil fouled plugs could mean the oil is getting into the cat as well as coating the O2. Also oil fouled plugs could be a problem themselves. Valve guide seals may be bad. Worse than the somewhat typical over night seepage.