Brian----hope you did not mean me---I was not trying to imply that it was your fault.
Randy-----had the exact same thing happen to me.
left it running to run into Alberstson's for a minute.
When I returned the van was already on it's way across
the parking lot and headed for the hiway.
It lost all of it's steam on a rather steep incline before it got to the hiway.
I would imagine the look on my face was priceless "Where the hell is that van going??"