Why do I get micro-stutters during stealth scenes in Unknown 9?

I felt totally ripped out of the immersion during stealth missions when sudden micro-stutters hit. I tried enabling High Performance mode in the Windows Power Plan, but while max FPS rose, my minimums stayed around 40 FPS, meaning the cooling response was just too slow. I then used the GamePP Fan Curve Configuration Panel to lock my pump speed at 85% and set radiator fans to max at 65℃. RTSS showed frame times dropped from 16-32ms to 11-14ms, and HWMonitor confirmed temps stayed at 64-70℃, while AIDA64 tracked a steady 2200-2400RPM pump speed.