speedometer reads 25 MPH fast

Have a 99 Voyager.Had to give it a jump due to a dead battery. Started and runs fine but the moment you turn on the key the Speedo reads 25 mph. Installed a new battery and left all connections undone overnight just in case. No change. Used a scanner. No codes. Pulled the gauge fuse.No change.Unplugged the main computer module by the underhood fuse box. Waited 30 min. No change. Don't even have to start the van just turn on the key and bingo-25 mph.Took it out on the freeway and went up to 95. This pegged the speedo but did not return it to zero.I'm done.Help!!!

sounds like you have an instrument cluster failure. Nothing you can really do to fix the cluster itself except to replace it.