[429mustang]

Sounds like your starter is absorbing too much heat from the headers/exhaust while your driving around. I'd go get a heat shield or thermal wrap from jeg's/summit. My car did the same thing for a while, then I broke an ear off the starter and got a new one, it started fine even after I drove around for a while. The problem did start to come back though after a few months though. I'd say it;s possible the timing may be too far advanced, but that would probably do it even when it was cold. Definitely try and insulate the starter.