My 1997 Ford F150 XLT seems to be having issues with the starter and/or the flex plate. I go to start up the vehicle and it sits there and grinds, and occasionally starts, which sounds to me like it could be the starter. I replaced the starter twice so far. I’m stuck at this point and looking into shims to see if that would help. If anyone has any info or anything that could help me out please let me know!

 

Replace the starter solenoid because it's probably the OEM component and well why not....it's OLD. Everything fails.
Also, check the battery. Clean the posts

 

Are you talking about the solenoid under the hood or on the starter. If your talking about the one on the starter it has also been replaced twice.

 

I would replace the complete starter again, (for the 3rd time) not just the solenoid
We used to replace brand new solenoids at the dealer with another brand new solenoid due to several recalls on the OEM part
I would also use a breaker bar and a socket to rotate the crank 1/4 turn and re try it for that noise
If the noise stays the same after moving the crankshaft position (new different teeth on the ring gear) replace the starter
If the noise is gone, replace the ring gear
Also, if you do replace the ring gear, (flex plate in your case) replace the starter again just for GP's
That way, you will have new drive teeth engaging the new teeth on the new flex plate

 

A weak battery can produce those results. I would clean/charge the battery first to see if that is the problem. A jump start might also indicate if it is a battery problem.

 

Yeap, always check the LOW HANGING FRUIT first