When you install the edge and select one of the preloaded settings it will read the rear end gears from the pcm and program it in there right?

 

If you use the "canned" tune and do not create a custom tune it will use the values from the PCM. If you even say yes to the "Create Custom Tune" prompt then you must go in and set BOTH the correct tire size AND the actual gear ratio of the truck.

 

This is true...you can only change settings if you choose the "custom settings",other than that it will keep the original factory setting.