I am also experiencing severe framerate drops and audio/video desynchronization with my disc copy of TWD on PS3. I have a freshly fragmented, serviced, wiped cache, restored, etc. file system, and a recently cleaned Blu-Ray drive that plays other games and movies without incident.
It is an older 80GB PS3 that came with MGS4 on the game's launch (CECHExx.)
I am not running a dynamic theme, and have recently cleared up space on the HDD (pre-defrag) so that I believe there is close to 30GB of free space on the console.
I have tried everything I can think of to get the game to work, which is quite a bit, considering I work in QA. Please let me know what steps I can take for my wife and I to play the game again.