I have used the Yellow Box to calibrate the speedometers on my motorcycles with great effect. The box comes, for motorcycles, as a plug-in-play unit. You simply use GPS to determine how far off your speedo is and adjust the dip switches to get the propper correction factor. Since most motorcycle speedo's are WAY off stock it has been a popular item. I am getting new tires soon, bigger ones, for my 4Runner and wondered if anyone had used something similar for their 4runner? I probably could use a Yellow Box without plugs if I could figure out the wiring for the Toyota Speed Sensor.

 

see Schaeffers website. He's got a similar gizmo on his 3rd gen.