Windows 98 is the last time I dealt with IRQ conflicts, lol
Incidentally, I run a 27" 1440p 144hz primary via HDMI, and a secondary 27" 1080p 60hz over DP
And your CPU and GPU temps are fine you said .. how is your airflow thru your case? You have to keep your VRM's and RAM cool too
You failed to list your power supply make/model ...? and how did you test it to rule it out?
Make sure your motherboard's BIOS is up to date
Make sure you have the latest AM4 chipset drivers installed from AMD.com
Do you have issue's with your PC IF you run just 2 sticks of RAM in slots A2/B2?
Are you overclocking anything?
Have you tried simply setting a more aggressive fan curve? and/or just doing an auto undervolt to see if that helps at all?