Very strange and spontanous drop in performance when in fullscreen in Standalone game

Yes, the problem occurs only on that resolution and on fullscreen and stays even with level transition. After tinkering I figured out that:
-If the input on my monitor is DVI, I have NO problems AT ALL, even when I don’t have other cables plugged in(like an HDMI cable)
-If the input on my monitor is HDMI AND I have another cable plugged in my monitor (works both with HDMI and DVI cables), I have NO problems AT ALL
-If the input on my monitor is HDMI AND there is NO other cable plugged in my monitor, the problem happens