Deathloop FPS drops from 60 to 35 after an hour on my B450M, how do I fix this?

This motherboard is a total disaster under heavy load. After playing for an hour, my minimum frames would tank from 60 down to 35, which is just unacceptable. The VRM on the ASRock B450M-HDV R4.0 overheats way too easily, triggering a limit that makes the CPU clock swing wildly between 3.6GHz and 3.0GHz. I tried undervolting in the BIOS, but that just killed my performance further, dropping my minimums to 30 FPS—a total fail. I ended up adding some small aftermarket heatsinks to the VRMs and tweaked my case airflow to push the VRM area fan speed to 80%, while disabling HDD power saving in Windows. HWInfo showed the VRM temps drop from a scary 90-105℃ range down to 78-84℃, and the drops stopped. I actually had a scare where the heatsinks almost shorted something because the space is so tight, but some Kapton tape fixed that. Now the CPU stays at 72-78℃. Stress tests show the clock curve is finally flat and fans are steady at 1400-1600 RPM.