How are you finding out that your speedo is off? Thought I found, in the vehicle settings, a way to adjust the speedo. When I had found it, I thought it was cool. Then I went to a lot of the known speed indicators, in school zones and a few "hot spots" on Edwards AFB, to see how accurate my speedo was/is right out of the store. Some were showing about 0.5MPH, but most were showing dead on.
If I stumble across it again, while playing with my vehicle settings, I'll post the directions to get to it.