I have a 2003 Chevrolet Suburban 1/2 ton z71 with a 5.3 liter v-8. Several months ago the speedometer started to act up. While driving, the speedo would show a speed that was much different than the speed of the vehicle. Usually, this will show slower than the car is actually moving, but sometimes the speedo will peg out (120 mph) even while the car is stopped. Now the oil pressure gauge will also act strange, showing very low oil pressure. If you turn the vehicle completely off, and then on again it will often, but not always, correct itself. Sometimes, after correcting itself, the speedo will get "off" again during some point of the trip. Is the gauge cluster bad, or is there something else that might cause this?

 

They are commonly known for bad stepper motors in the gauges.
somewhere i read GM warranties them up to 80k miles. im not sure how that works.
I just replaced mine in my 05 with a white face SS 06 style due to the same reason.
Carl Clowes of Digital Dash Solutions in conneticut is reccomended by alot of people to repair clusters.
Look for his ebay store. He also sells parts kits if you can do the repairs yourself.