Hello I will help you with your question,
If you have the plastic rock shield off this is half the battle.
Remove the negative battery cable
Remove the two large bolts from the starter housing and catch any shims that may be in the starter to block mating surface.
The starter will come down at this point and you have to support it while you remove the large battery cable and the small switch wire from their terminals on the starter.
Reinstall without the shim and without the plastic rock shield.
Try the starter if it grinds install the shim and try again.
You may need more than one shim or you may have to shim only one bolt. This is a try and see situatiuon.
Those are my instructions, these are GMs
When removing starter, note if any shims are used between the starter and mounting surface. If shims are found, reinstall in original locations. If starter is noisy during cranking, remove one .015 inch double shim or add one .015 inch single shim to the outer bolt. If starter makes a high pitched whine after engine start, add .015 inch double shims until noise ceases.
- Disconnect battery ground cable, then raise and support vehicle.
- Remove starter braces, shields or other components that may hinder starter removal.
- Support starter and remove mounting bolts.
- Lower starter and disconnect solenoid wires and battery cable.
- Remove starter from vehicle.
- Reverse procedure to install.
Let me know if you have further questions about this