I installed a Speedcal about a month ago to correct for 4.10's, finally got the switch setting right and the speedo was dead on. However, driving to work today I took an exit ramp and out of nowhere the speedo went to zero but the odometer kept spinning. Then when I got back up to about 60 mph the speedo shot up and read very high (at about 80 mph it read 110) It is acting like the switch settings are off in the SpeedCal but the obviously werent touched. Anyone have an idea of where to start looking here?