Starter Problem How do I properly shim a starter for a 1998 GMC Sierra C1500 (5.0L). I have a bolt missing and it has caused the starter to be slightly misalligned? I do not know how to shim the starter properly once I replace the missing bolt in the starter.

This is the ring gear on the flywheel that is damaged - they can eventually wear out - however more than likely a faulty starter motor Bendix drive gear or incorrect starting can cause this damage.
You will need to remove the gearbox to replace the ring gear.
There ring gear needs to be heated to expand it for it to be replaced.

every thing you did is about supplying power to the starter and nothing about checking the ground circuit. check the ground circuit as you may find the problem there.

sounds to me like your starter isn't shimmed correctly common problem for the 5.0l and 5.7l. your starter isn't meshing with your fly wheel correctly and causing unnecessary strain cause the problems you stated.

That is not generally an issue, and I don't know how you could check clearance after the starter is bolted up.
As long as you have the correct starter and the starter shims, if the old or original starter had shims, then the clearance should be right. You can check the starter drive gear that engages the flywheel-if it is worn badly, replace the drive gear, or the starter if you don't want to take the starter apart.

On some models of general motors starter shims are required to maintain
the recommended clearance between the starter and flywheel.
If not, then the starter will hang on the flywheel after motor is started and
damage it (The teeth are bottoming out when this occurs). They sell starter shims at
the auto parts store.
Hope this helps.

Possibly turning the key while engine was running or by hitting something or by tightening bolts to much where is the Crack around the bolts to check install the starter and use the shims and torque to specifications the Crack also could be for a missing shim and cranking while running

4.3L Engine

1. Remove or disconnect the following:
   
   Negative battery cable Bracket and shield Wires Mounting bolts and shims Starter

To install:

1. Install or connect the following:
   
   Starter Mounting bolts and shim. Torque the bolts to 33 ft lbs. (45 Nm). Wires. Torque battery wire nut to 89 inch lbs. (10 Nm) and ignition nut to 18 inch lbs. (2 Nm). Bracket and shield. Torque the nuts to 53 inch lbs. (6 Nm). Negative battery cable
   
   
   Fig. Exploded view of the starter motor-4.3L engines.
   
   

1. Remove or disconnect the following:
   
   Negative battery cable Bracket and shield Wires Mounting bolts and shims Starter

To install:
Install or connect the following:

Starter Mounting bolts and shim. Torque the bolts to 33 ft lbs. (45 Nm). Wires. Torque battery wire nut to 89 inch lbs. (10 Nm) and ignition nut to 18 inch lbs. (2 Nm). Bracket and shield. Torque the nuts to 53 inch lbs. (6 Nm). Negative battery cable


Fig. Exploded view of the starter motor-4.3L engines.

Hope help with this (remember rated and comment this).

The starter should have come with shims. You may have to adjust the new starter with the shims, so that the bendix, starter drive, meshes properly with the ring gear.
As long as the battery is fully charged it should turn the engine over.
Please let me know what you find.

was the starter recently replaced? if yes, needs shims to aling the gears properly. This is a trial and error process. If not, well you need a new starter.

You can take out the spark plugs and turn the motor over by the frt at the bolt that holds the harmonic balancer(or lower pulley),with the plugs out it should turn over pretty easy.