84 ranger starter problems

Tried to start and sounded like starter was working but nothing else. So I ztook starter off had it tested, they said it was good. I got home cleaned it up (should have cleaned it before taking it) and it was falling apart on the inside, springs where falling out, it was bad. took it somewhere else and bought a new one. I put the new one on, it then started right up. Thought i fixed the problem i was happy. The next day go to leave for work and it was doing the same thing as before. I checked the flywheel and it looked fine even though the old starter was demolished. can push start it sometimes but not allways. when I do push start it and it dosnt work it sounds like the fans and everything are spinning but no power,gas ect.. ( I was told to hold a heat gun to the starter and that could fix it)
Thanks in advance for any solutions you may offer.
84 RANGER
2.0 ENGINE
5 SPEED TRANS