This is an issue that is plaguing some users both in the NVidia and AMD camps. Builds with both Intel and AMD cpus as well.
When connected to steam and Rockstar social club the game stutters every few seconds. Sometimes it's every 10 seconds, sometimes more often. This all started with the small patch that followed the "Ill Gotten Gains" patch. Here's a link to Rockstar's forum: https://support.rockstargames.com/hc/communities/public/questions/204366187-GTA-V-frame-rate-suffers-massive-drops-since-1-27-patch-PC-
Here's a link to a steam forum: http://steamcommunity.com/app/271590/discussions/0/594820656447632634/?insideModal=1
and here's a video of a guy playing @ +120 fps showing the stutter. https://youtu.be/JIQuDG9I9ck
So most of us are thinking this is attributed to an anti cheat drm added to the game in the recent patch.
I've opened a ticket with Rockstar, but they won't give me a straight answer. Their troubleshooting steps were laughable. First telling me to lock game to 30fps(half/double vsync). Then forcing it to run in DX10. Last bot not least they wanted me to update my Radeon drivers, but I was using the gta 5 game ready 15.4 drivers.
The stutter is gone when I unplug my network cable, with steam in offline mode, while playing single player. I repeated this several times to rockstar in my ticket. Again, the game runs flawlessly with the network cable detatched, but has the random stutter online with social club. Even single player is effected, while connected to social club.
My last response to them was that if it was a driver issue, how come the game runs flawlessly with the network cable unplugged? I have yet to get an answer, so if anyone knows anything, please let me know. I've just been playing single player offline since the patch. I just wish Rockstar would come out and tell us what's going on, and stop giving me ridiculous trouble shooting tips.
((FX-8350 on water, asus R9-290x DC2 OC, 16gb ram @ 1887mhz 8-9-9-24))