Workin' on my boat...

Ok, here is the problem I am having and the steps I have taken to correct said problem:
Occaisionally the starter "drags" and will not turn the boat over. After several tries, it usually fires off, but not always...
1. I have charged and tested both batteries=tested good
2. I replaced the starter with a brand new unit.
3. I replaced the dual battery switch.
4. I changed the grounding location from the bellhousing to the starter.
5. I cleaned and inspected the battery cables.
6. I have "jumped" the starter at the solenoid, it just clicks..
7. Pulled my hair out.
8. Stumped my toe kicking at it----j/k.

If I have missed anything, please chime in & let me know! I would like to have this thing running reliably soon!!

************BREAKING NEWS************* I found the problem!!
I pulled the starter & guess what? It's defective!! Brand new from O'Reilly's too! It will not turn when directly connected to a fully charged battery via jumper cables. The solenoid just clicks. I can bypass the solenoid and the starter motor turns, but does not kick out the starter drive. I will get the starter replaced tomorrow & also I will replace all cables with heavy duty 2 guage cables....