The worst "oh S---" I've had with losing control was down shifting and hitting 2nd instead of 4th. Almost lost it. (wet and rainy) rear end dancing like yours was, but I knew what caused it and got it corrected quickly.
Hope you can figure out the cause so that you can avoid/correct soon.
Yes, I'm curious to know too..
Bin there and done that at about 80 mph, almost sideways.
You guys and girls are the best!! I really appreciate everyone's input! I sent the links to the vendor who did my transmission, so hopefully he can shed some light into this.