CVar gxVSync

This cvar determines whether Vertical Sync is enabled or disabled. Vertical Sync caps your FPS at your monitor's refresh rate. See CVar_gxRefresh for more information on refresh rates.

Default Setting

 * 1

Possible Settings

 * 0 :Disabled
 * 1 :Enabled
 * 2 :Enabled - caps fps at half the refresh rate

Changing this setting
In-game, go into the Graphics Setting screen Hit Esc, click on the Video tab, Check Enable Vertical Sync.

Or

In-game, type the following /console gxVSync setting

Or

You can exit wow, open the Config.wtf file, and add the following line: SET gxVSync setting