Found on website for Grand Cherokee (closest thing I can find for a hill hold feature)
Hill Start Assist
Hill Start Assist1 helps prevent vehicle rollback when starting a vehicle from a stopped position on a hill. It maintains brake pressure for a short period of time after the driver releases the brake pedal and steps on the accelerator to begin moving forward.
1 Criteria must be met for Hill Start Assist to activate:
Vehicle must be stopped
Vehicle must be on an 8% grade or greater hill
Gear selection matches vehicle uphill direction
Hill Start Assist will not activate if vehicle is in Neutral or Park.
****the last item is probably why it rolled, must have put it in neutral by accident. See post below:
Anton Yelchin's all too predictable "freak accident"
Now I'm starting to understand why my BMW has a separate "Park" button on the shifter (pushing forward and back only allows R, N or D).