Hy coolchevy, did you replace the starter drive? It sounds like it is not working all the time. The other thing that can happen is, the drive does not mesh with the flywheel teeth, but the action of your foot on the starter pedal closes the switch contacts on the motor making it spin. You should check your flywheel teeth for burrs that may be stopping the engagement of the starter drive with the flywheel, hope that helps.
