Issues with external display

I have a new 27" iMac with a Dell U2713HM external display connected with this dual link DVI to Thunderbolt adapter. I have a couple problems.

There's a purple line along the left of the screen when running at 2560x1440. At other resolutions it disappears.

More importantly... after the iMac has turned off the screens due to inactivity, when I touch the mouse and they come back on, the Dell apparently comes on slower so everything that was on that screen moves to the other. The display then comes on and the resolution is something ridiculously low until I unplug the Thunderbolt adapter and plug it back in.

I'm guessing the problem is that adapter but I'd like someone to tell me that before I buy another. I've already spent $30 on a HDMI adapter only to find out it doesn't support my resolution and then $80 on this one.

 

The answer: the U2713HM has a displayport. I'm an idiot buying that adapter.