Speedometer goes crazy

I have a 2003 Avalanche. Once every month or so while driving 70mph or so the speedometer goes to over 100mph. If I stop it might go back to 60mph then when I take off again it picks up from there. If I go 30mph it will register 90mph. I can get it to go back to zero if I stop and start the motor while in park. Every time I do this the mph will decrease about 5mph until I get to zero. Is this a bad speedometer sensor or a bad interment cluster?

It is the cluster. GM just announced a warranty extension on certain models. Call your dealer and see if you are covered. This is a very common problem.

Thanks txdealer. Just looked it up and they are supposed to replace the cluster if the vehicle has under 70000 miles. Mine has 42000. I found out that this has been a problem with GM vehicles for a while now. Not only with the speedometer but also with all the gauges in the cluster.