I HAVE THE G3258 I KNOW THE PROBLEM! dont worry your CPU, GPU MOBO and whatever else are fine, it because the G3258 is a dual core CPU and GTA V NEEDS 4 cored to run or you will get a heavy stutter effect, now this can by mostly fixed by 1: getting a quad core CPU or even a dual core with HT (Core i3) and option 2: use NVIDIA control panel to get GTA V vertical sync to "half" that will cap you FPS to 30FPS and overclocking your G3258 will help a LOT as well, even a small OC like 3.8gHz or 4.0gHz will be a large performance boost, i have my G3258 to 4.2gHz and a 30FPS cap on GTA V and in story mode i see no stuttering but i do see some it i play online with about 20 other people. here a video i made to show how to use the NVIDIA control...