The GM SX9 esc has a 130 degree F shutoff in the circuitry.That is why it's shutting off.I use one in stock buggy and never have issue's with it.
If you use it in a stock or mod enviroment where heat can be a issue then you will have nothing but problems.
The SX12 does NOT have this problem.
Contact Horizon and talk to repairs.Send it in and they should switch it for you.
On the GM V12 surging.I havent had this problem but with as many as they sold Im sure there are some bad one's.When you send it in do you send along a Index Card explaining what it's doing?In their test they might not be finding anything.
*****Look me up on Ebay. I will have alot of stuff going up as 7/7/2016. User name is Dalracer.**** This is going to be a BIG ONE!!!!!!
Just wanted to say Thanks to RcTech for all these years of Great Information.