[MetaEngineer]

Double check all connections between battery and PDP. It raises a red flag for me when you say the voltage dips low even when the bot is idle and that the CIMs are not burning hot after 10 minutes of driving with them "stalling" as much as you describe.

Loose nuts or crimps at connectors, breaker, or PDP can cause brownouts like that, even with fully charged batteries. Likewise check the connections at the battery terminals, though I suspect the problem is on the bot since it happens with multiple batteries.

That said, you should also look at the threads Dr. Joe posted and think about the gear ratio of your drivetrain and your lift. The kit chassis you have comes with a 10.71 to 1 gear ratio, which is a little weak for grippy 8-inch wheels. The 12.75 to 1 gear ratio option may help you a bit at the cost of some top speed.