I don't know if it's truly variable but on my second ride of the day Friday morning I experienced the same thing. I've ridden TTD probably 50 times over the years and that's the fastest I've even gone over the top hat. Oddly it was a weird run all around. We rolled out into the "parked for launch position" and then the sound effects, etc. shut off and they rolled us back into the station, announced to the crew to re check the train/restraints and then we rolled back out into launch position and had that crazy ride. It was about about a 3/4 full train.
1.8 (m/s I believe) is the speed reduction, it varies usually between 1.0 and 2.3/2.5 depending on what the max is set to (it starts the season at 2.3 and when it gets warmer they increase it to 2.5). You cannot change it, it's all automatic. The only time it changes after it reaches the max for the day is if you start launch boosting trains, or in diggerg56's case, when it rolls back the speed reduction automatically drops to increase the chance the subsequent launch will crest the hill. The crews know ways to manipulate it, such as loading a train special to get a rollback, but unless they were only loading partial trains, the speed reduction shouldn't drop. My guess is it could have just been acting up that night as it sometimes does as it can be unpredictable at times, especially if it is cold.
This makes complete sense. It was the last train of CoasterMania and they had been fiddling with passengers and trains for a few minutes. I couldn't quite catch it but now I think I had heard "It's at 1.8". The maintenance guy kinda smiled and shook his head as workers piled on. Thanks for the info. I hope I'll get another one of those someday.