I have a 98 silverado that i am tuning and I have new tires and according to the company site for the tire it is a 31.5 in tire but in the tune it is registering as a 30.96 and is locked out to be changed. If you go by the gps the speedo in the cluster is too fast and the tuner is 1 faster then the GPS. Is there a way to unlock that so i can correct it to get it dead on for when i sell the truck to the gf she has a lead foot and that couple mph could save her a ticket?