Ford Repair: 1992 F150 Speedometer, mileage vehicles, high mileage

Question
Dennis,
I have a 1992 F150 with a 5.8L and E40D tranny.  The speedometer bounces above 50 mph.  I have replaced the speed sensor in the rear end (the old one was ate up).  The bounce is still there and the new sensor is in good shape.  Additionally, the cruise control is also having trouble maintaining speed on the highway but I think that these problems are related.  Any ideas would be greatly appreciated.

Answer
I am pretty sure your truck has a PSOM, which is the abbreviation for the speedometer module in the instrument cluster. The PCM and cruise get the speed signal from this module, not from the speed sensor although it is part of the system. Ford had lots of problems with PSOMs, especially high mileage vehicles.