86 S10 misses when hot

My sons 86 s10 2.8 thrttle body 150,000 mile . It starts missing and backfirring when it gets realy warmed up. not just alittle warmed up. may have to drive it for an hour and alot of stop and go. Checked the eletronic spark controll module thing in distributor and it checks out okay. Not sure where to go from here? sometimes in cold weather the problem does not happen at all. When it starts doing this you can keep it running smooth if you go easy on throtle,but if you stomp it or even a little quick exeleration it seems to jump timing. I'm going to change wires and check slack in chain and put in new plugs cap and button. If I can get him to part with the money!

I don't know when your son's last complete tune up was, but I've seen bad ignition wires that behaved that way (work fine cold, fail when hot), and it is particularly bad if it is the coil wire because it affects all of the cylinders. But it could be a lot of things. Assuming you are not looking to put a lot of time or money into the car, perhaps try replacing just the coil ignition wire as a fast and cheap possible solution. If that noticibly improves the problem, replace the rest of the wires and do a complete tune up.