Speedo Problems

[braebyrn]

On my 03 Sierra 2500 my speedo is intermitently showing slower speeds than what is on my GPS. It is anywhere from 10-30 miles per hour off. Most of the time I have been driving for over 3 hours or more when it starts to go down.

Luckily I use the cruise control, but the other day I found myself doing 75 in a 55 and I couldn't figure out why I was passing everyone.

I have the hypertech programmer on it.
Rick

[More Power]

Return everything to stock, then try to dulplicate the problem. If you can, you may have an instrument panel cluster problem. A Tech II scan tool can be used to verify whether the speedometer tracks what the ECM is seeing.

Jim