Display problem with new MBPro 15 retina and DELL

[sartos]

I can't work out if I am doing something fundamentally wrong here. I have my shiny new 15" Maxed out Retina Macbook, only really just plugged it in and using it... I have it hooked up to my Dell U2713HM which supports up to 1440 resolution... but this doesn't work very well at all with the new MB. It won't give me a choice of resolution and chooses a crappy one. The most it will let me select (sometimes) is 1080p. Other times it gives me a wierd resolution. I am using a miniDP to DP adapter just like in my old macbook pro (which incidently still works perfectly with this monitor), but the new one...😡

It all started going wrong when I tried to extend the desktop to the Apple TV... and no matter what I try I cannot get it to work again. I have reset the SMC etc...

I don't get it. Everything worked perfectly with my old 2011 MBPro.

Is it the Thunderbolt ports? Is it unwise to use them as MiniDP ports?

Thanks in advance

 

[sartos]

Screenshot

This is the wierdness I am getting in the display settings. There would normally be several resolution choices in the Scaled section...