[AZKen]

Lots of thoughts. Too many to list. Can you describe misfire? Stumble? Not sure if it's a fuel stumble or ignition "misfire". When noticed? how often? backfire? Idling rough? only under load/acceleration/hills? Don't know your abilities or experience with motors. First thing is determine gas or electric. There are deeper issues also, valve timing et al. Please confess to anything recently done to motor or gas tank. Anything. Daily driver? Weekend driver? Been sitting long time?
You may be able to isolate a particular cylinder by pulling each plug wire off one at a time. If one does not change motor, that is the one that is missing....or check each plug to see that it is firing properly. Or without removing anything, you can use an inductive timing light on each plug wire to watch the light and see if it pulses at a constant rhythm or matches the misfire.