The other day I bought a Samsung U28E590D, not specifically for its 4K features, but primarily because more screen real estate over the Samsung 23-inch I had would be helpful in my work. My card is an old one, a Radeon HD 6870, but if I understood this table from its specs pdf, I should at least be able to get 1920*1200 out of it. That increase would actually be OK for my work purposes.
Despite this, I seem to be stuck at 1920*1080 - the same resolution I had with my 23-inch monitor.
I have installed the Samsung monitor's driver, updated the AMD Radeon driver, and have spent much time since Friday trying to find a fix. The monitor has 2 HDMI inputs, I've tried both. I've also tried unchecking the GPU upscaling option shown ticked in the above screenshot. Is there no way to get a display resolution higher than 1920*1080?