Check the fuses in the fuse box under the dash. You most likely have the dreaded rub through from the OD switch wiring. The easy way to test this is to replace the fuse and then take the truck for a ride. If everything is working then quits again it is the wiring in the shifter that has rubbed through. The only other possibility is that the instrument cluster needs to be replaced. The VSS going out will not make the odometer go blank.