I asked about the parking pawl because I was very optimistically hoping that the shift linkage had perhaps came loose when shifting to park but I didn't read your first post correctly to see that it happened while you were actually driving it.

I'm guessing a spring in your valve body broke so there is no engagement pressure or one of the solenoids in the transmission died causing essentially the same thing. If they say it's either, let me know because for what it will cost for them to repair/replace with OE parts, upgrades will be the same or similar price.

Also, got your PM so I'll call you shortly.