1990 454 runs rough pull #2 plug wire off and runs smooth or pull #4 and it runs smooth. Was over heating its at a shop put new a thremastate 165 and new water pump and new fan clutch . took for test drive it when from cold to the middle. Runs rough? Any one know why, could it be the head gasket between 2 and 4.

 

What do the plugs look like?

 

suitie

 

Only pulled them 2 plugs.
Tested them 2 cly with air he said they did not lose any more then a new motor.