On a truck like yours its a small sensor that drives it by providing output information of the transmission to the PCM so its probably the speedo itself, it is replaceable, but we use a tester to check all three things out plus the wiring, but the way your describing it is like the meter in your dash is bad.
The vehicle speed sensor mounts on the end of the transmission and it signals the engine PCM, this is the speed and odometer memory and can be scanned for codes and monitered to isolate the exact problem.
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Tuesday, January 5th, 2010 AT 10:48 PM