speedometer problems on 1999 Ford F-250 Super Duty

my f250's speedometer recently quit working, it would start and stop for a couple of days. have changed the sensor on the rear differential, still does't work

Really need to scan the data stream and see if the computer is seeing the signal from the rear speed sensor, if so, it may be a dash problem or a Central electrical Computer problem that is not letting the rear speed sensor talk to the Instrument Cluster.