Just experienced this fun issue -- driving along at 70 mph when all of a sudden I lose power and the transmission downshifts to 4th gear (aka transmission limp mode).
Call the dealer to find out there's a TSB on this -- when the temp is very cold and you are driving at high speed for over an hour, there is a valve that does not perform; the oil flow is restricted. There is a new valve that can solve this issue.
All-in-all, not a huge issue if I was notified ahead of time --- I found out today when I was driving in -20F weather. This is not a time for the car to not work.