Alright, I don't suggest shotgunning/purchasing parts at random for a solution but I'm thinking dist pickup. got another dist you could sub in for a quick test? (that'd be much easier than tearing down a dist to R&R the plate). plugs would act up right away and plug wires likely would the same way but not always but this sounds like a system upstream from them that is causing a major issue when it heats up (like the pickup or the box). EDIT With more thought I might borrow some plug wires & check the plugs both of which would be much easier