Dave, sounds like exactly the same thing that happened to my controller and I was running it close to its limits.

I was running hornets 2 18V drill motors on 24V pushing the controller to its limits. I blew through two of the controllers before getting a refund (one original, one replacement).

Depending on when you purchased the controller and from where I believe you may be able to get a replacement or refund.

It seems the sabretooth does not like to be run on overvolted motors.