Q about starter heat shields

[82 GT]

First of all, every guy that works on his own car should at least have a timing light.
If your timing is too high, your engine will struggle to turn over even when cold and damn near impossible when hot.
My guess is that your starter is getting heat soaked now that you have shorties and I'm assuming flowmaster exhaust.
Get rid of that big bulky starter and buy a mini starter for a '94GT.
I had this same problem with starters when I got my flowmaster exhaust and shorties. Since I switched to a mini starter, my problem is gone. I'm willing to bet that you have the same problem.
Trust me, get rid of that antique starter you have.
I can tell you what wires you need to switch around if you decide to go with a mini starter from a newer mustang.