.gig files from 2.54 load fine, but I've had some trouble with 2.54 .gsp files (such as templates). They seem to load o.k., but when I hit play, the computer will lock up or BSOD. The workaround is to load the .gsp and before sending the giga computer any MIDI, write down the instruments and mix settings, then close the .gsp and build a new one from scratch using your notes. I haven't had any problems with .gsp's that were built in the newer versions-
It's been a while, but GS2.5 gets uninstalled. Just follow the instructions, which are very straightforward.
If there are problems with uninstalling GS2.5, you can run the GigaClean utility.
Once installed you have a ten-day window to register it. Don't run GigaClean after installing GS3, or you lose the ten-day deal. Don't try to save or restore the registration either, until you get your numbers.
Tascam will e-mail you your serial number - it won't be in the box. You need that before you can register it.