Alright...figured something out. The Dakota Digital Universal Speedometer calibration chip has been used by many Toyota owners for a while, with good results (average fix to w/in 1-2 mph). Since the Xterra also uses an electronic signal to the speedo, this chip should work on the Xterra as well. Although Dakota Digital states that this should not be used on ABS-equipped vehicles (the ABS system uses an electronic speed signal and the factory-programmed tire diameter to calculate proper tire clamping power and deceleration speed), Toyota owners who have used this chip on their ABS-equipped Tacos and LandCruisers say they haven't had problems. You will, however, have to understand that this will change their braking characteristics (I am looking into whether or not the dealers can re-program the ECM and ABS control computers to account for different tire sizes, but I doubt it). This mod can be found at Dakota Digital SGI-5 Keep in mind that this will take some time to configure to accurately portray your actual speed.