What is a "power stage"? BTW I may have solved the mystery. I thought that there was a possibility that she could have easily hit the winter mode button for the transmission which would would give you similar symptoms, especially if starting from a stop on a hill. So I put the car in winter mode w/o her knowing it and let her take off from the same hill and she said it felt the same as when she had the "problem". This button is easy to press accidently especially if you tend to put things on the console when you drive. The orange arrow lights up but some don't know what that means and it resets when you turn off the ignition. Problem has not happened again so I will keep my fingers crossed :)