Starter will not turn or disengage

When the truck would start the starter wouldn't disengage. Replacing the starter initially at least turned over and catch the flywheel. After awhile, it would just make a winding in grinding sound as if the flywheel and starter where clanking or something was over speeding but not catching. Replace the ignition switch and ignition key lock (that was fubar anyways) and replaced the solenoid. Tried again, and same thing. So dropped the three month old starter and seen it was fubar as the Bendix would slide up and down easily. Put a new starter in and first time it started fine but didn't disengage. So tried second time and starter did disengage like it was suppose to. Tried third time and back to the winding/grinding sound but no catch so I'm pretty sure that starter is now toast though the battery is at roughly 11 volts but the starter acted strong. After removing the old starter, the teeth on the flywheel looked fine. Also metered the the line from the solenoid to the starter and it read 10.7 volts only when the key was switched to the start position otherwise got 0 volts. The two heavier wires on the outside of the solenoid has constant voltage regardless if the key is even in the ignition and the voltage matched the battery voltage (which I don't know if that's good or not). I Just do not know what's going on. Any suggestions?