Why would they not have the option to use custom resolutions? I can't even play the game with these 4 presets that you can only choose from. Is there some way to edit an ini file or something?

Finally found a fix if you need custom resolutions.

Open up your Fallout4Prefs.ini file ( documents/users/mygames/fallout4 )

bMaximizeWindow=0
bBorderless=1
bFull Screen=1
iSize H=
iSize W=

Look for those settings and change your heigh / width to whatever settings you need. Then just load the game.