I had a similar experience while "exercising" my SRT last summer. I was exiting one freeway and merging onto another. I punched it midway through the ramp and was well over 80 by the time I slid into the far left lane. I was not shifting manually. When I realized how fast I was going, I lifted. I heard a THUNK! and when I went to reapply some throttle, I got nothing. The tach topped 5k before I realized that the transmission had disengaged. I had enough speed that I was able to coast back across two lanes of highway traffic and up the next exit ramp into a gas station. I shut off the car and waited 30 very long seconds. When I turned it back on, everything was fine and it hasn't given me any grief since.

Based on the descriptions here, I think I lifted right at the moment the transmission was going to shift. Perhaps the mixed signals triggered the shift to neutral. Whatever it was, I didn't care for it one bit.