I clocked mine after adding 32" tires with me new lift. When I was at 70, GPS said 74 I believe. Changed out to a 32 tooth gear 70 on the speedometer is 69.6 on GPS. But then again, I'm anal like that. I have to know Exactly how many miles I get out of a tank amongst other things.
$44.98 through our quadratec guy here.