Checking the odometer?

[Powerwagontim]

Hi Guys,
I am looking at an 02 Silverado 1500 with 35,000 miles. The truck has a transmission temp gauge. I suspect the instrument cluster was changed to provide the trans gauge. My question is, can I take the truck to a dealer and have them plug into the computer to see if the mileage on the odometer is correct? I do know that the odometer on the cluster is self contained, ie the truck computer does not reset the gauge odometer if the cluster is switched, so does the computer even know the mileage?
Thanks for any help,
Tim