I would try swapping spark plugs around first to rule out a bad plug. From your description, it sounds like you've ruled out most of the other ignition system. Typically, if the engine dies when pulling one plug wire, another cylinder (or two) isn't firing properly. The engine RPM'S should noticeably drop, then return when the wire is reattached. If little or no change, that's the cylinder to concentrate on. You can also check the header pipes and see if each seems to heat up the same. You can use a spray bottle, your finger (ouch!) or a non- contact thermometer (works best). I'm guessing your issue is fuel or compression related...
