Automatic Transmission problems of the 2008 Porsche Cayenne

On my 2008 Porsche Cayenne s ( purchased in March 2007) I have at least 3 times experienced a incorrect downshift initiated by the automobile in all cases the car/computer obviously wanted to shift down to a lower gear ( going up a steep hill at highway speed, traversing a steep parking lot at low speed) etc rather than shifting one gear the car seems to have shifted 2 or 3 gears at one time the engine revved to about 5000 rpm within the red line limits- very noisy and disconcerting I exited the problem by manually shifting to neutral which cleared the problem then back to drive I reported the issue to my dealer who obviously could not reproduce the very intermittent problem, he also says he checked the computer log and could not find any report and that there no service bulletins relating I think that this could be a serious safety issue being potentially a major driver distraction.