I purchased a Dell UltraSharp U2715H. This has a 2560x1440 resolution.
I have a MacBook Pro Retina (early 2013). I now have the following issue getting to this maximum resolution.
1) HDMI If I attach the monitor through HDMI I only get a resolution of 2048 x 1152. I first thought it was the HDMI cable so I bought a new one, no effect. When connected through HDMI everything else (close lid etc) works perfectly.
2) DisplayPort cable The Dell also came with a Mini DP to DP cable. If I use that cable it works perfectly when I startup the MacBook from scratch. So, the beautiful full resolution of 2560x1440 is there! HOWEVER, when I close the lid or the MacBook goes to sleep it somehow "loses" the monitor. The Mac still thinks the Dell is there. It is there in the menu and you can even go with your mouse to the second monitor, the Dell itself however remains completely black. So the only way of getting the monitor to work again is fully power off the Mac and then power it on. This is of course not a workable situation.
So, does anybody now how to solve this, either through a working HDMI or a way to get the DP connection to work normally.