Tim
I agree it's got to be a calibration issue. I saw the wheel sensor when I was greasing the front suspension and everything looks completely as it should. That's what's frustrating because re calibrating an electronic speedometer should take minutes but I can't access the recalibration menus.
Wheels and tyres are standard 15" by 6" , unless opting for stainless wheels has some mystical impact on the rolling radius.