Re: Why reinstall Win3.1?
Actually, I blame both Rockstar and still Windows 10. There are reports of newer machines running Ryzen 7, with a super-duper RTX 2080Ti, where no cores are fully pegged, neither is the graphic card, and still, the game stumbles below 144 FPS, sometimes 90 FPS, when it should be blasting to the limit of the monitors / graphics card.
It is a known problem for GTA Five engine, poor utilization of multithreading, being a 6-7 year old engine.
My own machine is irrelevant, given all the reports on Reddit, and Steam. The stutters seem to get worse in full lobbies, where the network chip is being hammered for some folks (hence it is stealing resources from the main cpu to run, drivers to blame), which is also a documented problem. Denying the lowest core to the game improves the situation a lot, because of these aspects.
In fact, Windows 10 is saving the cake here, allowing to reallocate executables by hand, because older stuff is unable to share, a core still can't handle multiple programs peacefully. It is so evident that first suggestion is to run the game in high priority, and the second is to deny one core for it, let it hog the other 5 cores / 10 threads.
Newer games are being designed to spread over several cores, instead of running a spaghetti code for a single core... remember that the PS3 was the first videogame with 8 cores... and GTA was created on that era, with the PS3 limitations in its zero-day design. Today, next-gen GTA is blocked from the PS3, exactly for surpassing some features that the old consoles can't handle, while others can't be bypassed without re-making the game from the ground up.
Video encoding is a fully parallel task, where you can send each chunk to a core, so the programs were quickly updated to take advantage of it. Games run on several rules and AI, which are not divorced from each other easily after the first design, being unfair to compare both.