Bronco starter over heating-HELP!!!

I have a 1986 Ford that after I drive it around a little bit it I start to hear a grinding noise when I it is started. I thought it was maybe the starter was bad so replaced it. Kept on doing it, so replaced the flywheel. Still no fix. Shimmed the stater, replaced hot and nutrual wires, replaced sylonoid, and put a cover on the starter. Thougjht maybe the exhaust was making the starter hot and no that is not the propblem.

Once hot the start just free spins and I am lost as to what it could be. Flywheel is fine, stater tests good, and once it is cool starts fine.

Any suggestions?

351W
4x4