The *.tun files contain the entire 512K or 1Mb of PCm flash memory (i.e. calibrations AND operating systems) as well as a bunch of meta data, comments, history etc.
If you opt to do a calibration only relfash, then EFILive just picks out the 96Kb of calibration data from the *.tun file and flashes that into the PCM.
If you opt to do a full reflash, EFILive reflashes the entire 512K or 1Mb of calibrations AND operating system into the PCM.
The "special" case is the EFILive custom operating system base *.tun files. These *.tun files have deliberately had "labotomies". We zeroed out the entire 96Kb of calibration data and forced the calibration checksums to be invalid. That means after you have full-flashed one of EFILive's custom operating systems, the PCM will enter dead poll waiting for a valid calibration.
Then you need to perform a calibration only reflash from one of your own *.tun files that matches the new operating system. i.e. a *.tun file from the GM operating system from which the EFILive custom operating system was derived.
Ross has just finished writing a tutorial on how to upgrade to a new EFILive OS. It contains a list of all the GM<->EFILive operating system combinations. It should be available tomorrow.
Regards
Paul