Hi, so I came across this posting having the exact same problem as you. Could not get my XL2411Z to run at 144Hz, and it was a real pain in the a**... None of the suggestions above worked for me so I fiddled around a little myself.
First, bring up this picture
http://www.datapro.net/images/dvi-config.jpg (creds to KevinAr18). The cable I use is a DVI-D dual link, bottom right, with the same pins on both ends. Plugged it in the GPU slot that had the same port and the screen went all blurry when setting it to 144Hz in windows (1080p still). Ended up trying to plug it in the DVI-I slot in the GPU, bottom left on the picture, and for some weird reason this worked. Now it's running at 144Hz and no problems.
If your GPU doesn't have such a port, I don't know what to do, sorry. But hope this helps. Thread might be dead aswell, atleast I tried!
Specs: BenQ XL2411Z and GPU: Gigabyte Geforce G1 Gaming GTX 970. And the cable was from a third-party(produced by Belkin).