Is anybody else having issues playing on this resolution? I can't seem to get it to work.

Got it working with the following fix:

If you’re running a 4K or ultra wide monitor you can enter custom resolutions in the Fallout4Prefs.ini file located in your documents folder.

bTopMostWindow=1
bMaximizeWindow=1
bBorderless=1
bFull Screen=0
iSize H=XXXX
iSize W=YYYY

The UI doesn’t scale, so keep that in mind!!!