Yeah probably 16 gb of ram would be better. But first let's try something else.
1.
Try running the game in admin mode
GTA V may stutter if it cannot have certain permission of certain game files on the system under user mode.
-Right-click the shortcut of your game’s launcher and select Properties.
-Click the Compatibility tab and check the box Run this program as an administrator. Then click Apply and OK to save your changes.
-Relaunch the game again and see if it works properly.
2.
Also, you can disable the full-screen optimization feature in Windows 10 to fix the issue.
-Navigate to your GTA 5 game folder.
-Locate the GTA5.exe file, then right-click on it and select Properties.
-In the Compatibility tab, check the box before Disable full-screen optimisations. The click Apply and OK to save your changes.
-Relaunch the game and see if the problem has been resolved.
3.
Turn Off VSync
The feature, however, is known to cause stuttering issue for many players. You can turn VSync off in GTA 5 to see if that helps.
-Go to GTA 5 Settings.
-Click Graphics.
-Find VSync and turn it OFF.
-If it’s already OFF, try turning it ON, then restart your game and turn VSync OFF again.
Now, restart your PC and GTA 5 once again to see if the problem still exists.