I just ran it in the dirt. Good news is the motor temp was only 125 degrees and that is all out on some dry dirt in 90 degree ambient air.
It behaved much better in the dirt. Still using the stock tires too, saving the new rubber for the track. I didn't get to experiment with the slipper because I ran out of juice before I decided to try. It will still step out on the throttle or on the brakes, but not really anymore than I'd normally expect with a 2WD.
I feel like an idiot testing on the street and allowing that to confuse my results.