I'm facing the same problem with an Intel Motherboard (DH67BL) equiped with a Core i5 3470. I'm connecting to the monitor using HDMI cable (came with the monitor). I installed the latest Intel drivers.
I used Intel's control panel to create the custom resolution (2560 x 1440 x 60). It all seems to work fine, but when I select the custom resolution, the image keeps "shaking" or "trembling" and I am forced to revert to a lower resolution. I have tried enabling and disabling interlaced mode but the problem persists. Any ideas?