Well, yes I have one of those on the positive side, but it is temporary and I have checked voltage drop and it is not the problem.

However, I think I found the problem. Decided to try voltage drop testing the negative battery cable before pulling the starter. Not sure why I hadn't yet, but long story short it was the cable to block connection. It looked fine, but I clipped off a good chunk, shoved it under the bolt and wow. Big difference. Started and restarted 4 or 5 times without issue. I will be investing in some new cables asap, and verifying my start issues are gone. Feeling a little stupid for missing that earlier, but thanks for the help everyone.

And so, on that note, where's the best place to get battery cables these days?