Stuttering After New Patch - ATI Card

[msu68stang]

My game was playing fine before the newest patch was released. Now if I'm on DX11 it will play OK for a few minutes then start stuttering. I've played with the v-sync and triple buffering settings. It seems that with DX11 on and v-sync and triple buffering OFF it will work but of course the v-sync messes up. DX9 is playable but slows down severely in City Hubs. Are there any other options I can try to be able to use DX11 instead of DX9? My specs are below.

Windows 7 64-bit
Intel i1-2600 Quad Core
Radeon HD 6970 2GB 256bit with the latest 12.4 drivers
16GB DDR3 2133 RAM

Thanks in advance