There is no official 4.3 firmware, atleast for ATT. 4.2 and 4.3 are only incremental updates to 4.1.
SGS3 i747 sporting Task650 AOKP(Jellybean 4.3) backed by KT747 kernel
If I have helped you a THANKS is appreciated but not expected, and if a problem was solved a [SOLVED] tag in your post title helps better the community
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