Recently I bought a ultra-wide monitor which a really weird but useful 21:9 aspect ratio.The only way mac would support this if i get a mini displayport to displayport adapter.
Since some orders take weeks for souq to fullfil.I decided to the use the single DVI cable from my older monitor on the new one.Once I plugged it in I faced the same issue the mac would only render only upto Full HD or 1920 X 1080.After a quick googling I found that SwitchResX can solve this issue.
But for some reason every time I create a custom resolution of 2560 X 1080,SwitchResX would not save it and if it did it would say not installed.I tried this a couple of times.I even deleted all the SwitchResX files and even uninstall SwitchResX from the menu bar.
Even setting the resolution was really difficult, after rebooting a couple of times I finally got it working with the following settings.
To get SwitchResX to save the settings.Follow the instructions in these instructions:
Create a new user on the mac
Install the SwitchResX application,this will start the 10 days trial.
Create the resolution profile and save it.
It should prompt you to reboot the mac.Please do so.
And Voila the resolution is should now present on your original user’s SwitchResX.Now you can select it in the current resolution tab.