overcloking P2815Q

hello all !

i would like some help for overcloking my display 1440P 30HZ to 60HZ plz
i have cru 1.3 and crimson driver 16.11.2 on a HD 7970 hdmi connected

i put a custom resolution for 144OP 60Hz, my display tell me he is at 60hz but it's not smooth like 1080p 60Hz.

thanks !!