Truck has issues starting

In search of any ideas on whats going on with this truck I just got. I got myself a chevy k1500 1994, its had a new starter installed new battery new alternator and it will start sometimes. That being said it seems like the starter is grinding on the flywheel and im thinking thats why sometimes it refuses too start. I get it too start every now and that being jumped and just installed a new battery and it wont seem too turn over the stater barley trys before it seems too just stop. It has plenty of power. Thought it might need shims but it looks like theres a lip that would prevent the starter from being able too be shimmed. iso ideas before ripping into being I dont have much free time…

If starter motor is spinning, but engine isn’t (during cranking mode, key in start), some problem with either starter gear, flywheel/flex-plate ring gear, or spacing between them. Possible fault with starter motor internals as well, but less likely. In any event, starter motor will have to be removed for a look-see , ring gear teeth, starter gear, etc.

If you’re not sure whether or not starter motor is actually spinning or not, ask your shop to help you make that determination. If starter motor isn’t spinning, problem could be electrical rather than mechanical. First electrical test, when key is in start , voltage at starter’s “s” terminal (thin wire) should be 10.5 volts or greater.

Problems out of the box w/aftermarket starter motors not uncommon by reports here. If you think that’s the problem, try oem replacement.