Any Diablo's registering 10% faster and 10% more miles??

After putting the OEM rims back on the car and doing a mileage check (by mile marker and checking with GPS) remember I am an Engineer, I am still reading on the speedometer and odometer 10% greater numbers that real distances and speed. Fixes anybody?? I have told Nelson Lamborghini about this problem and they are researching it as I will be doing service soon with them and I would like to have some solutions in mind.