If that's your only problem then the speed sensor is most likely faulty on the transmission. It's not uncommon at all on your van.
Let me know if you need more help.
The instrument clusters are equipped with a self diagnostic test feature to help identify electronic problems. Prior to any test, perform the Self-Diagnostic Test. The self diagnostic system displays instrument cluster stored fault codes in the odometer display, sweeps the gauges to the calibration points, and bulb checks the warning indicators. When the key is in the ON position with the engine not running, the MIL will remain illuminated for regulatory purposes.
The CLUSTER CALIBRATION table contains the proper calibration points for each gauge. If the gauge pointers are not calibrated, a problem exists in the cluster. If any gauge is out of calibration, replace the cluster.
If a segment in the odometer does not illuminate normally, a problem exists in the display.
If a segment in the transmission range indicator does not illuminate normally, a problem exists in the display.