Hi,
Sorry for the delay in response.
We were researching on this and seems that the issue here is the WD19TB.
We would like you to dual link DVI-D output to get full resolution out of a Cinema Display.
We suspect the DisplayPort (DP) output from the dock is the standard Single Link DVI output (DisplayPort - Wikipedia). A dual link DVI-D output would require an active (powered) DP output.
We would like you to test this by removing the dock and plugging the Cinema Display directly into the Thunderbolt or HDMI ports from the Latitude (Latitude 5500: Visual Guide to your Computer | Dell US)
Regards,
Aditya Roy
Microsoft Community – Moderator