If you haven't updated your drivers yet then you could try that. The only thing I can think of is that your CPU might be bottlenecking your GPU. I have a FX-8320 CPU and a EVGA GTX 770 4GB GPU and I know for fact that my CPU bottlenecks my GPU. When I play games on ultra with my CPU at it's standard speed of 3.5 GHz I usually lose anywhere between 5-20 fps at times compared to when I have my CPU overclocked to 4.25 GHz. The GTX 770 is a high-end GPU and is more than capable of running Far Cry 3 on ultra at 1080p with MSAAx8 with 30+ fps (probably higher on average). That being said, you need to accompany the 770 with a high-end CPU. You should probably get an i5-4670k or better.
I play Far Cry 3 as well with a 770 and get 50+ fps on ultra, 1080p, and on MSAAx4 so it's probably not your graphics card giving you trouble. You may want to look into overclocking your CPU or buying a new one if updating your drivers doesn't work.
Here's a comparison between your CPU and a somewhat higher-end CPU:
http://cpuboss.com/cpus/Intel-Core-i5-4670K-vs-Intel-Core-i5-3350P
I really thinks it's your CPU keeping your fps down and not your 770.