There is a tattle tail feature on the LMM's that keeps track of the programming/flashes. This was relayed to me by the shop foreman and friend at the local GMC dealer.
I recently did a turbo back exhaust and installed a "Spare" computer that was programmed mild upgrade/tow.
Hand calculated my mileage in town is up 1-2MPG on the highway 5-7 MPG increase.