I've got an 86' Trooper II, only 224K miles on it.
Right now it's my second vehicle, so it sits a lot and only gets driven maybe twice a week. For the last few years, it's had the weirdest ignition problem. If it sits a lot, and isn't driven much, the ignition will cutout at certain RPMs, usually above 2500. Like a rev limiter sorta. Anyways, a new set of plugs ALWAYS fixes it. Why? If I drive it every day this never happens. But every time I let it sit up a while or don't drive it all the time it gets this miss at certain RPMs and it won't go away unless I drive it a lot for a few weeks or put a new set of plugs. And I've tried like every brand plug available, OEM NGK's do the best it seems. Entire ignition system is new, and in the past I've tried swapping anything in the system around and nothing makes a difference except a new set of plugs.