My odometer just plain quit on my '93 LC Now it's about 300k and the speedometer is on the blitz. Nothing when I start out. On the freeway about 55mph it starts to suddenly work accurately. If I drive for 20-30 mins. at that speed, then it will work correctly at all speeds until engine shut off. If engine shut off and drive again, same thing happens, IE., nothing until 55mph and then it works well. Any Suggestions? Thanx in advance