I think it's time to individually test pieces in a totally different environment. If you have something wired wrong and you're smoking the CC-M boards, it's going to get expensive! This is why I have this test board, it has connections to test almost any TMCC board including the ERR CC-M and RS-Lite boards. This is my go-to for individual board tests, then I start looking at the environment once I've determined all the pieces are functional.
Yes, this grew a little at a time, it was a simple board when I started, but each time I needed to test a new component, I added connectors, etc.