Don't discount plug color as a clue. Intake gaskets could provide lean out if worn out as noted by others. If you have an infra red gun take some head temps. And BTW even new coils will fail at overheat. Of course I believe all AC engines are close to overheat, having measured 310F on my Intek. No I have not measured how hot a coil gets, but they have components in them that will only tolerate a certain threshold. Remember, too a lean running engine is much hotter .Not trying to torment, but you've got a tough one, right?