It has a reman. engine, new radiator, battery and much more. It starts right up the first time. During subsequent times after the first good start, it hesitates when it turns, but eventually starts. Starter and alternator tests came back fine. Mechanic still thinks it's the starter. Thoughts?
How old is the battery?
How close is the exhaust to the starter? LS 1,2,3 and even the new LT1's suffer from starter heat soak?
Not a for sure, but I have had failing starter motors behave similarly. You might consider one of these gizmos if you work on your own cars, found on Scotty's tool page and Amazon. It's well spent money IMO. Good luck.
Why does the "mechanic" think it's the starter if the "starter...tests came back fine?"
What could it be?