Remove the starter, put it in a vise, and bench test it with a set of jumper cables. If it spins freely at good speed and doesn't make the cables overheat, find the circuit problem between the battery and the starter, both hot and ground sides- - - -probably loose or dirty connections, or possibly a short.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!