If most people could see the parking pawl in most automatics transmissions they would wonder how it holds the car in park. I see guys with lifted trucks pulling boats and race trailers and do not use the park brake. Surprised more do not roll away.One of the weak links in the NAG1 design is the parking pawl...
The transmission was designed for an AMG 55 Mercedes.
It was always suspected the weak parking pawl was the reason the early Grand Cherokee SRT8 had a 3500 lbs. tow rating.. the parking pawl isn't designed to hold a trailer in park on an incline with or without the parking brake set.
My guess is that pawl snapped.