I have an 03 Sierra Duramax with 105k miles of trouble free use. The only Gripe i have is that the speedometer does not work. It started climbing to 120mph one day and it just kind of has a mind of its own. I have to drive the truck like its a boat (tachometer only). I know that at hiway speeds if I keep it around 2300 rpm's, I am traveling roughly 78-80 mph. I have to use the trip computer to dail in an exact speed when on cruise control. Anyone else have this problem? My wifes 03 Yukon also has this problem on occasion. hers will work sometimes.