Way off topic - I have a 2005 Chevy with a duramax - the cruise does not work - I have checked all the fuses - they are all good.  The speedometer will sometimes go wat out of whack - it will read 90 when you are only doing 30.  The odometer is not affected.  Is all of this related? I have not had time to take it in - it only has 75,000 miles - Any ideas on the cause?