Davids right on the filter, 60K interval, I would do it if you know it's over that. Sure it doesn't "have" to be changed, it's not like the engine is going to develop "mystery" problems right at 60,000 miles, but it's still a good idea to do it on schedule.
Another thought, since you're inviting ideas, is our old pal the overvoltage protection relay.
Also the distributor cap and rotor, usually these will be more od a permanent running problem though, not coming and going like this.
I believe I did have a problem similar to this that ended up having a partially plugged catalytic converter.
Gilly

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