I've experienced a few issues installing and updating GT6 from scratch, one update kept failing to install @ 14% and corrupted my install, turned out to be something ISP related, used another connection and it went through flawlessly,
After that, I managed to install the others in one go, but you do need to leave your PS3 on with GT6 launched when done, to initiate the in-game installation, which takes a few hours,