I am assuming it will be the guage cluster....they are know for going bad. I did find this on alldatadiy.com:
"The IPC displays the vehicle speed on the analog speedometer based on the vehicle speed signal from the PCM. The PCM converts the data from the vehicle speed sensor to a 4,000 pulses/mile signal. The IPC uses the vehicle speed signal circuit from the PCM in order to calculate the vehicle speed.
The speedometer defaults to 0 km/h (0 mph) if a malfunction in the vehicle speed signal circuit exists."
I sent you the tree by e-mail. You might try and see if you have any codes too. Also, IIRC a bad battery could cause stupid problems like this.
I just put this same thread topic up,trying to get people to respond. I have talked to dealers and to Chey Corp. and they don't want to recall it. This is a very common problem with chevy's. You need a new instrument cluster which will run $450 at a dealer because they have to reset your mileage. If you call(888)327-4236, or go to www.odi.nhtsa.dot.gov. This is the National Highway Traffic Safety Administration and report it we can hopefuuly get this recalled.
Yes I did. I found a place on ebay in Connecticut. If you look up instrument cluster repair. I sent it to him, he fixes it the same day and ships it back, with a 1 year warranty. You pay through paypal, and you can still drive your rig without the cluster while you are waiting. Works Great!! Chevy wanted $450, not to mention you without a truck. I sent the cluster out on monday and got it back on saturday.