Yukon Odometer / Speed

I have a 2001 Yukon SLT that has a speed issue. The speed always registers about 8% fast (shows 70 when going 65). I have taken it into GMC 2 times and they have found no issues but replaced the unit just in case.

When I bought the car, the sticker said it had Denali wheels (which should be 17s?). I only have 16s - I have asked the dealer and they said that they are Denali style wheels. What ever those are?

Has anyone heard of these issues?

Does anyone know how to check the speed (tire size) setting to see if they have it set for bigger or smaller tires?

Thanks