I've got a IMac 27" from 2011 hooked up to a Dell U3014 external via a mini port to DVI adapter hooked up to the Thunderbolt port. The max resolution option is 1920X1080 instead of the Dell's native 2560X1600. Am I missing something? Kind of a waste of a 30" monitor! BTW, I updated the os to 10.8.5 with no difference. Help?