My spedo is off by about 1-2mph (reads slower) and the odometer reads about 1 tenth of a mile more every 16 miles than you have actually traveled. It's not a big deal but you would think with these new trucks it would be right on.

I have the stock tires on my truck 265 70 17s. I'm just going to use the tuner's tire size feature to match my speedo to the GPS to fix it.