Maximum total monitor(s) resolutions? Precision 7550/WD19DCS

Hello,

I have a Dell Precision 7550 running Windows 10 connected to a WD19DCS dock. Overall it performs well.

Currently I have 3 monitors connected to the dock (the dock has 2 DisplayPort and 1 HDMI port):

• HDMI: 1920 x 1200
• DP1: 2560 x 1440
• DP2: 2560 x 1440

WalMart has a sale on a nice ultra wide QHD monitor at 3440 x 1440, so I thought I'd get that to maximize the screen space so I bough the monitor.

Here's what I want to have:

• (1) HDMI: 2560 x 1440
• (2) DP1: 3440 x 1440
• (3) DP2: 2560 x 1440

But when I connect them, the large monitor (2) is forced to a maximum resolution of 2560 x 1080. I tried moving the monitors around to the different ports, and the result is always the same - one of the monitor resolutions gets derated.

Does anyone know if this is a limitation of the docking station? Or of the laptop? Any workarounds available? 

If not, is there maybe a better docking station I can get to achieve my maximum tricked-out monitors? Where can I find out the limits of monitors and resolutions?

Thanks in advance for the  help.

-- Steven