having some starting problems with my 68 camaro. Have replaced the battery, battery cables, and starter but still getting a very slow turn over. Voltage on battery is 12.9, but drops down in the 10v range while cranking. I have traced wiring, but so far have not found any bad connections. Seems to be worse on a warm engine vs. cold engine. i am not running headers, and heat shield still in place on starter. When I replaced starter with a rebuilt one, seemed to help for a few starts, but now right back to square one. Even when I put a booster box on with the battery still get a slow turn over. I am thinking I have a bad starter, but just wanted to get some opinions before I pull if off. Thanks and merry Christmas to all.