I have never been so happy to have gotten my laptop wiped and upgraded to High Sierra, the new macOS, installed!
Sometime last year, I upgraded to macOS Sierra and I lost scaled HiDPI resolutions beyond 1920×1080. Additionally, the display had some sort of padding such that the display did not reach the full width and height of the screen.
Today, I got my 4K monitor capabilities back. And, I am so giddy!
diversiev 