I found the issue was with the monitor. By changing 1 setting the resolution was fixed. See [here](https://discussions.apple.com/thread/6814406 "fix apple monitor res"):

>On the Mac: System Preferences > Displays > Under the Display tab set the Underscan -> slide to OFF! (This ensures it is in the default position)

>On your Monitor: Image Control > Custom Scaling > Overscan ---- OFF!