ive had a misfire and boosting problem on my car for a while

it would idle fine, when cold it was perfect, then after around half hour of driving it would have a mis at 1800 rpm and up untill 2000 rpm. and wouldnt go above 3500. took it somewhere and they changed my chip to another one, changed rotor arm, checked gaps etc everything and was still the same

then they put another ecu with another chip in whice was in the workshop and it was fine, so i thought i needed a new ecu.

got a spare one so changed the chips over (l6) put the new one in and went for a drive. fine when cold, shitty when hot.

it was getting hot where the ecu sits in the dash so took the ecu out for 10 mins and left outside to cool down. plugged it in and made my mate put it on his knee insted of in the dash.

the misfire and boosting problem has nearly gone, only happened twice on a 2 hr drive.

so my question is, could my chip be breaking down when hot, or both ecus? or do i need to somehow heatproof where the ecu sits to keep it coolish?