While driving tmy rpm gauge will start to fall down to zero and the car will stop. After it sits for a few minutes it will start up againwith no problem. This only seems to happen when I go over 50mph. I took the car to the dealership and they couldn't find anythign wrong with it, their best guess was the crankshaft relay. They said they drove it around and could not get it to repeat the problem, I am guessing they never got it over 50mph. I didn't have them replace anything yet, anyone have a simliar problem or any suggestions?