Disable V-Sync in the game menu. Instead, use your GPU's control panel (NVIDIA Control Panel or AMD Software) to force V-Sync or set a Maximum Frame Rate cap that matches your monitor’s refresh rate.
By applying the fix and lowering PostFX , you should see a much smoother experience while hunting through the jungle. FAR CRY 3 - How to BOOST FPS, FIX STUTTER AND LAG
Even years after its release, Far Cry 3 remains a masterpiece of open-world gaming, but its optimization for modern hardware can be... finicky. If you’re experiencing frame drops on Rook Island, you aren't alone. Disable V-Sync in the game menu