Starter could be pulling excessive amps. Not sure if the auto shop checked that. More amps means more voltage loss between the battery and the starter. Low voltage means slow cranking. Corroded terminals, corroded wires also increase voltage loss. Check both ends of the main cable from the battery to the starter, and the engine ground straps. Missing engine ground straps can increase voltage loss.

Thanks for the tip. I知 going out today to go over the engine grounds. I know the starter wires are all good on both ends as well as the ground wire from the battery.