just rebuilt runs bad

Beware of the mopar performance piston stops. there are a bunch of them out there where the threads do not match the spark plug holes. Chrysler is trying to pawn them off on customers instead of scrapping the bad ones and getting a good batch out there. Take it out of the package and test it on a good set of heads before buying. I hear the comp cams ones have the same problem. Buyer Beware....