i have an LG 34GK950F which i used to pair with a RVII in DP 3440*1440@144. I sold the RVII and now am temporary using an old 290x. Problem is, the max refresh rate i can set is 100hz (other than 60 and 75).
I tried with uninstalling drivers in safe mode, resetting bios and so on.. the HDMI port seems not to work (even if it was working on an old 1920*1080@60hz display) and so is GPU scaling (goes blank). I also get hardware acceleration black screen with netflix, streaming services that uses it in browsers and some games (devil daggers goes blank after a while, children of morta and blasphemeus don't).
I had the card running on a secondary system and it did have a custom cooler on it that i had to remove due to incompatibility with the CPU cooler on the main build and it ran any game with no issues at all. I thought of it as the card being old and needing a better cooling system than the stock one but..