I had problems with Mavericks in getting full resolution in my monitor Dell U2713H (connected to a Mac Book Pro). I used this solution from this site to fix the problem:
I downloaded the file from http://embdev.net/attachment/167830/U2713H_U2713HM_Mac_EDID_override.zip, and after copying it to /System/Library/Displays/Overrides and rebooting, my display was showing again its awesome full resolution.
I did it again when I installed Yosemite but it does not work. Any idea to fix this problem for Yosemite?. Otherwise I will downgrade to Mavericks again. Thanks!!