Gta 5 lagging randomly on a good computer after playing on it for ages fine.

[Roskaters1]

GTA 5 was running fine for days until randomly recently its frames went from 120 FPS+ To 10-30 and rarely 40. Specs are Rtx 2070, I7 10th gen, 16 Gigs of ram.

Have reinstalled game and nothing changed, No matter what settings game has the same lag, Game is 100% set to the GPU, Reseted settings and that also did nothing, Not Background Processes as I ran windows without anything on-start, Not the Power Settings or any Driver issue / Update needed. No overheating issues and ventilation is fine {40-60 Celcius}, Get better fps on games with more requirements then GTA5 yet still lag on GTA5 more than them, It is not anything to do with game corruption because I've reinstalled everything multiple times {GTA5, Rockstar Games, Steam}, Not a plug issue {Have tried other plugs}, All cables plugged in correctly. 100% Not a hardware issue, Have 60GB of storage free, Ram is running fine and allocated to GTA5, Nothing is underclocked/overclocked. Do not want to reinstall windows due to lots of important files I can't afford losing.

Please help, I'm willing to gift games to people if they can find a fix.