My 2004 Chrysler 300m seems to be downshifting then upshifting as I drive along at 60-70 mph! it shifts back and forth so quick the tach doesn't even move however sometimes the speedometer does drop a bit. This happens randomly with no consistancy, sometimes I'll drive 30 miles and it won't happen then it starts for a couple miles.The tranny seems to shift fine around town,stop light to stop light , corners etc.... Only have the problem at highway speed. Any help, ideas,suggestions?