Low FPS issues are back?!?!?

I recently noticed I am having low fps issues again... I have a GTX 1060 3GB, i5 7400, 16GB ram, 256GB ssd (league is on ssd) and 1TB of storage. Ive always had around 140 to 160 FPS but now i don't know why I am getting only around 60 sometimes even 30.. I play on borderless and max setting, I am running a dual monitor setup with a 29 inch ultra wide (main for playing league and other stuff) and a 27 inch. I have VSync off also tried turning off anti alias but that didn't help. Ive tried to go into my properties of league and disabeling full-screen optimisation and some other stuff... But nothing seems to work but this only happens on league.. on all the other games I play I get a stable 120FPS but league just caps out at 60 and just laggs... Ive also noticed when I go into game I start off with 144FPS but the it lowers to 60 after about 20seconds. And my CPU usage just goes to 80 to 100% and my game just laggs while it shoudn't be doing that because my pc isn't bad or anything... My friend has a pc with an i5 4460 and a GTX 970 and atm he is getting more FPS then me... like WTFFF Plz someone help me if you can. I am just done playing league if this is just gonne keep happening. (Sorry for my trash english) Thanks in advance, Kevin aka FluffyNidalee