Why does my GPU downclock during intense MGS Delta battles?

Intense battles in MGS Delta dropped my FPS from 144 to 90 due to voltage drops. I tried increasing power limits, but it caused reboots. I used GamePP Power Plan Switcher to enable High Performance mode and BIOS optimization. AIDA64 verified voltage stability at 11.9V-12.0V. Frame times stabilized at 8-10ms. I verified the setup works perfectly now.