Could you please tell me your hardware specifications so I could deduce what could be causing the problem? Iv'e played tons of Far Cry 4 and I did experience a very minor drop in FPS while driving at high speeds. I guess you could say that it is a little GPU demanding. The stutter could be caused due to overheating, high CPU usage, or weaker hardware.
They're also a couple of fixes that can be found on the internet, such as:
Open My documents > Open Folder My Games
Open Folder Far Cry 4
Open the GamerProfile.xml file with Notepad
Find DisableLoadingMip0 = "0" and change it to DisableLoadingMip0 = "1"
Find GPUMaxBufferedFrames="0" and change to GPUMaxBufferedFrames="1"
Source: Reddit
You should make sure FC4 is using all your CPU threads, and make sure no other programs are open in the background. If your PC is overheating, clean out the fans or replace the thermal paste. Try update your graphic drivers if all else fails.
Hope your problem gets rectified soon