An on-screen tire size correction solution is very high on our priority list right now for development.
The reason currently that it is $100 for 3 tunes is due to the files currently being written by hand, and delivered as a full custom tune. Basically, it ends up being the same amount of labor as if we were building a tune for a truck with extensive hardware modifications.
Our method of recalibration doesn't involve just one module- both the engine and transmission files are changed. The benefits in this are that not only is the speedometer corrected, but all shifting parameters and N/V (related to axle ratio and tire size) load changes with the engine calibration are corrected likewise.
With the time spent on the latest V3 updates and 6.7L tuning development, it has taken longer than originally intended to get all of this incorporated into the Phalanx Console on-screen, but it is coming