I think SAMI has a BUG. And when you add mods with SAMI, it don't rebuild the archive.
It's better and safely to use IMG Tool 2.0, cuz you can add mods, edit cars etc and you can REBUILD THE ARCHIVE.
Rebuilding is most important, don't forget !
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Freezing:
How exactly freeze GTA SA? When you start a new game, or when you load a game, or what?