New XPS 13 with external monitor not getting anything over 1920x1080

I have the new XPS 13 (2015) and Dell UltraSharp U2713HM. No matter how I connect them I can't get anything over 1920x1080 to be available for the screen resolution (for the U2713HM).

When I connect my XPS13 to U2713HM via miniDP -> DVI-D (should be dual link) I get 1920x1080 max resolution showing in Windows.

When I connect my XPS13 to U2713HM via miniDP -> DP the monitor is recognized but it is disabled and I can't get Windows to show anything on it.

When I connect my XPS13 to U2713HM via HDMI->HDMI via the Dell USB3.0 adapter (DA100) the max resolution I get is again 1920x1080 (and the HDMI cable is high speed).

How can I diagnose where the problem is?

Thanks!