I'm having issues getting my 4K TV to detect 3840x2160 as a valid resolution in fullscreen. The max detected is 2560x1600. I've managed to work around it like so, but I think this is a bug: I have a 4K LG TV and a 1080p monitor connected to my Nvidia graphics card. When both displays are connected, the max available fullscreen resolution on my 4K TV is 2560x1600. Note that I'm not using Extend or Duplicate here, just the 4K TV. If I physically disconnect the 1080p monitor and restart the game, the max available fullscreen resolution is 3840x2160.