I'm wondering if it's the traction control thats kicking in, instead of SS.
When rolling backwards while in forward gear(drive or 4,3,2,1), something kicks in, not sure what. Whatever it is, it pulses brakes like abs, forcefully enough to stall motor.
Example: when four wheeling, climbing a hill, i didn't quite make it to the top, I released brake pedal, but left in 1st gear(auto), and after traveling five feet backwards, something engaged brakes enough to stall motor and scare the crap out of me.
I can recreate same effect in my driveway, just by letting truck roll backwards while in forward gear. It's very unnerving, it kicks in so hard that it stalls or nearly stalls motor.