D3100 not displaying 1440p?

Based on the specs, I should be able to use my Dell S2716DG monitor with my D3100 at up to 3840 x 2160 @ 30 Hz, regardless of how many monitors I connect (1, 2 or 3).

I've updated the D3100 driver and the S2716DG driver and I can only display 1080p (at 50 or 60hz, don't see a 30hz option) regardless of which port I use (DP or HDMI) and regardless of how many monitors I use (for testing purposes, I'm only trying to get ONE to work).  In the resolution drop-down, I only see 2048 x 1152 as the only option higher than 1080, and when I select it, the screen goes black.

I know it's not the cable or the monitor, since I have tested both with other PCs.

Is the dock defective or am I doing something wrong?