left for dead 2 issues.

[dmxdex2020]

Ok so i am playing through the single player campaign. I never played left for dead 1 but i do like left for dead 2. Ok so when i complete a level on the dead centre and begin the second left the game just becomes extremely slow and choppy? i am using a 4870 x2 with the 9.11 drivers.

 

[dmxdex2020]

I find when cat ai is disabled i get horrible mouse acceleration.