Bodragaz

I just installed the EDGE Evolution Programmer yesterday. I noticed that my speedo and the MPH reading on my Evo don't match?! My speedo clocks in about 2-3 MPH greater than the Evo. Thus far, I have only ran it on the Transmission setting, but I did customize it respective of my larger tires. I did notice in the manual it mentioned that "to obtain a true speedometer reading, the gear ratio should be modified as well." Is this trure? Sounds pretty major.