I noticed that even with all addons turned off

For a while, I am struggling with game stutter. It's happened on WOW TBC Gold all my characters. The stuttering is not so "random" but rather reactive a lot of the time. For instance, I stutter every when I switch weapons (2h to shield and in reverse). I also struggle to speak when I am opening my stealth mode on my rogue, and also when I drop combat. It happens number of times, but more frequent event when there's number of things going on, such as in a raid setting. To examine this issue, I disabled all addons. The results show that the stuttering has become smaller, yet it still occurs. This raises the question of why it happens. It's not possible that my PC is the issue. I tried disabling addons, changing in-game video settings and reinstalling the game. Flashing new bios , and disabled hyperthreading were just a few of the things I tried. It's not working. Do you have any suggestions what could be causing this problem? It's really irritating, imagine that the entire screen is stuttering each time you switch from a shield to use spell reflect as a warrior in pvp, it's horrible.
Update The issue is that despite all the work I did , and setting my FPS at an amount that kept the card at a lower than 50 percent load, I was seeing flickering while running an Kara raid the other night. As such I decided to completely disabling Freesync and this seemed to solve the issue.

I disabled it on the monitors itself, both are the same brand albeit differing sizes/models, and also in my AMD GPU settings. It seems like this has solved the problem. I'll be keeping an eye out for any other issues.

Original Post The reason I'm here is that I've been experiencing intermittent flickering problems, but I'm hesitant to ever call it full on studdering, for at least a while. It's not constant often, making it difficult to identify. It was getting to the point of driving me crazy so I decided to research.

Long story short, it is only recently that Windows permitted multiple monitor refresh rates to be used after almost 13 years, Microsoft seems to have addressed an oft-ignored issue with regards to how Windows handles multi-monitor refresh rates. Windows 10's Desktop Window Manager, (DWM) resulted in frame-skips, and stutters when multiple monitors had differing refresh rates. The issue appears to be corrected by Windows 10's DWM 20H1, a version that supports hardware-accelerated GPU scheduling (WDDM 2.7). A Reddit user has shown this effect.

The moment I discovered this issue, I went from having an 144hz main screen and an alternate 60hz display to all my monitors running 144hz. This was due to the fact that I didn't wish to change my system and my 60hz monitor was due to be upgraded.

However in doing so I made the switch to a bigger main monitor , which meant my GPU was now operating an increase in pixels both at that high a rate of refresh. My GPU had to work, despite it being sufficient for Classic WoW. It was simply not capable of the job.

I noticed that even with all addons turned off, no whatever version of DX I selected, whether I turned VSync is either on or off whatever it was that my GPU was reaching its limit, the game would display a level of flickering at times. With all its lush vegetation and zones such as Nagrand my GPU could be overloaded to 100% at some point, which would eventually result in throttling.

It seems that the WoW engine does not like when the cheap Burning Crusade Classic Gold GPU will throttle my system. Even though my CPU wasn't sweating, I saw the flickering when my GPU was at its limits. The flickering would be aggravated by add-ons.