Well I tried the other batteries. Drove fine for about 6 mins then it started dropping to like 20% power like it hit the LVC. I checked the batteries with a multimeter and all the cells are 3.84 and 3.85 and the LVC for the speed controller is set to 3.2

So to recap

1st set of batteries: brown out issues, one battery will not balance.
2nd set of batteries: starts cutting power after about 6 mins like it hit the LVC. Before this weekend, I've been able to get about 13 minutes of runtime before it hits the LVC. These batteries seem fine.

Don't know if the ESC is going bad, if both sets of batteries started going bad during the same race weekend or if there is a bad wire somewhere. Problem now is I don't have any other batteries nor do I have a backup ESC to troubleshoot with so it looks like a may be making some purchases in the near future.