Scan the computer while driving and see if the vehicle speed shows up on the scanner.
Check for AC voltage back probed at the ECM between pins B10, a Yellow wire and B9 a Purple wire.
If the input to the ECM is OK, check for a good square wave output at pin B11, a Dark Green wire.
If the inputs to the ECM are correct and there is a good square wave output, verify a good wire between the ECM and the instrument panel cluster.
If OK, replace the cluster.
Electronic Control Module (ECM)
Instrument Panel Cluster (IPC)
Check for MPH in scan data.
Disconnect the Powertrain Control Module (PCM) 24 pin black connector, turn the key on, pulse the Green Vehicle Speed Sensor (VSS) output wire, pin B11 to ground.
The speedometer should move while this wire is pulsed to ground.
Test the Green wire from the PCM to the IPC for an open or short to ground.
Disconnect the cruise control module and the passive restraint module, check for voltage to return on circuit #389.
Circuit 389 - Open/short in the Green wire, circuit #389.