I have a re-occuring speedo problem. after driving at highway speeds for extended periods of time (over an hour or more during the heat of the florida day. the speedo will start to drop speed and end up pegged at zero. after stoping and letting the car cool down it will operate normally again. especially at speeds less than 50 mph. I have checked & repaired the connection at the rear axle sensor, removed & cleaned the sensor & removed the instrument cluster& looked for suspicios solder joints. Is the speedo head dead and need to be replaced or did I not check thouroughly enough? Any ideas out there? I am ready to go to the local pick & pull.