Have a 2001 350ES that keeps getting stuck in fifth gear. It had a new angle sensor installed a while back from the previous owner. If you run down the road less than a half mile in fifth gear it will shift back down fine, but if you go over a half mile or so it will stay stuck in fifth until you turn the key off and then back on. As soon as you turn the key off and back on, it will downshift just fine, as if something resets. I don't know if the speedometer has anything to do with it or not, but it is very sporadic on it's readings ranging from 0 to 99 while driving down the road.