I recently installed a Zex kit on my car and wanted a good plug to use. I switched from the stock Motorcraft plugs I always run to a colder plug, Autolite 3923's. The car has a BAD miss now and Im putting the old ones back in in the morning. They are gapped correctly and the little shims or rings are on the Autolites. What could have happened? I thought this is the plug of choice for the guys running nitrous. Whats the best plug to run all the time?? Thanks for all the help guys........