this will have to be scanned for codes to find the problem, as it can be amoduleor a few other things.

The same failure that is causing no speedometer reading is also causing no cruise control operation. The sensor you replaced on the rear diff is part of the antilock brake control(CAB) module's sensor network. The CAB transfers the vehicle speed information from this sensor to other modules in the vehicle through the vehicle's controller area network(CAN). The fault may be in the wiring between the rear diff speed sensor and the CAB, it may be in the cluster itself, or it may in the CAN bus. A quick test of the instrument panel cluster(IPC) is to simply turn the key to start and look for the IPC sweep test to sweep the speedo needle through its full range of travel and back to zero. If this happens as it should, the cluster is most likely okay.

We have had alot of trouble with a main connector in the harness that runs along the driver's side frame rail. Look for a large connector that breaks the harness right under the cab of the truck. Locate the connector and, after cleaning it with shop air, disconnect it and look for sings of corrosion and moisture intrusion. Clean it as necessary and reconnect it. See if this doesn't solve your problem.