You have an output shaft speed sensor on the top of the tailhouse on the transmission. If it fails though, you should get a code P0720. If you aren't getting any codes, makes me wonder if it isn't a problem with your cluster. May be cheap enough just to swap that out to see. I am not sure which of the two, OSS or the VSS sends the speedometer signal of the top of my head.
**EDIT** looks like the axle sensor they are calling a wheel speed sensor, so I think an assumption that the OSS would be the one to send a signal that will feed the speedometer, but like I say....when it fails, you should be getting a code...
Last edited by f250Jason; 09-22-2012 at 02:37 PM.