Does what the local Chevy dealer is unable/unwilling to do.
After swapping the rear end to a higher gear ratio, I took my truck to the local Chevy dealer to have the speedometer calibrated. They told me that they did not have the codes needed to reprogram to reprogram my truck and that they could no longer get the code. After plugging this little programmer into my computer and downloading the codes it needed, I had my speedometer calibrated in less than 10 minutes.
Do not expect too much
Did gain almost 2 miles per gallon, and the transmission does seem to shift better for towing my RV. No increase in torque or horsepower noted but with that amount might be tough to see. Read the instructions and follow them closely. I think that as long as you don't expect too much it will be ok