How to fix frame stuttering between 50 and 80 FPS in cities?

It's so annoying! Every time I enter Novigrad's streets, the frame rate jumps between 50 and 80, creating a jarring stutter. I tried lowering shadow quality in-game; it dropped the temperature by 3℃ but ruined the visuals, which felt like a pointless sacrifice. I used the GamePP Power Plan Switcher to set the system to High Performance and locked game threads to high-performance cores. RTSS graphs showed 15-40ms jumps were suppressed to 12-16ms, while AIDA64 showed 72-80℃ and HWiNFO recorded 110-140W. Finally smooth!