I removed the game and deleted all the game files including my saved games. When I reinstalled it, the game seemed to run great and I could turn settings up higher than I ever had done before, but then after half an hour or so, the laggy frame rates cropped their head up again. I thought it could be a temperature issue so I shut the computer down for a while. When I started Tomb Raider up again though, the laggy frame rates were still there. I'm unsure where to go from here so I've decided to uninstall the game completely from my MacBook Pro and play it on my (lower specced) iMac. It's a shame because the MacBook Pro runs rings around the iMac most of the time, but Tomb Raider seems to temperamental on mine. I would reinstall the whole system but it's too much hassle to go through especially considering everything else is working fine.