You have a GTX980Ti and you force the fps to 55 at 2560x1440? Why?
Let it run free.
Also, I do not know if it automatic or manual for Nvidia, but on the drivers have you checked if Gsync is ON?
AMD pops up a message when sees a Freesync monitor and you have to activate it. It doesn't work by default.
Im forcing 55 or lower in order to test this issue. There are games that brings the 980ti to its knees at 1440p once you enable eyecandy and where this issue is showing itself yet i cannot test it if i cannot control the fps. Therefor i use settings that gives me over 60 preferable 70 or higher and manually control the fps to see if i can find the cause and where it shows itself.
 
	 
  
 
		 
 
		
 but what you wrote doesnt work for me.
 but what you wrote doesnt work for me. 
 
		 
 
		 
 
		