MacBook Air performance has gone down

I recentely did a fresh install of snow leopard on my 11inch macbook air. About 2 months ago I got this game and it ran very well on my air, however now when playing it, it isnt usable it is very choppy. I wish it would just work, I loved this game D: would be 5 stars for the amazing game but until the performance is fixed I have to do 2.

Im boarddddd about StuntMANIA Reloaded