Starter Troubles

My alternator went out on my truck, so I bought a used one and it failed to, got a new one and now my starter doesn't want to engage into the starter, I put 3 new starters on the truck same thing, now new clutch, pressure plate, flywheel, and starter it still wanted to studder when trying to start, it is damaging the teeth on the starter. I have checked all my wiring and have 13.6 at the battery and starter.