are you throwing a cell when it does it? if so get the code read. you have 1 or 3 choices here.
60K....you might have a bad COP, you might have a bad plug, or you might have a faulty injector.
try to get it to do it and throw a code. moneys tight....been there done that. if it throws a code see which cylinder it is giving you the code. then switch COP's with another cylinder and see if the code will follow you or if it stays on the cylinder. if it follows you and moves to another cylinder then replace the COP. if it stays on the same cylinder that you originally got the code from, you either have a bad plug, or a bad injector. might be cheaper to replace the 1 plug until you come across some money in order to do them all. or do both. a Motorcraft plug is 8 bucks, and an injector ( cant remember but guessing its about 50 or so bucks from orielys )
hope this helps.