I have a 94 chevy lumina it runs on hot dry days dont run on muggy days i think it could be the coilpack..??

I thaught that it overheated again and that the heads warped again...but after sittin for sale for 3 months or so i went out when a charged battery and it started and still had all its power...mind you i did a head job pervious b/c it overheated and warped the head but that dont seem to be the case...i need some answers to why its like this.....and dont tell me b.c its a chevy and give me retated answers i want real answers...thanks...