Frame Rate Problems

So, i just played a ranked game, lost obviously, but, due to massive frame rate spikes and drops screen tearing and overall instability in the game client itself. Just wondering what is causing this because i'm running a 3.7ghz gpu and a 1070w/8gbs vram and 16gbs of mem. So as far as i understand running this game should be a complete joke for my build/PC. My build used to run this game at 400fps. Now, it runs it at 120fps(unstable/variable and i mean DRASTICALLY variable) Losing up to 100frames is a joke on this build settings mean nothing and neither does things being open in the backround host processes etc. Short story, wtf is wrong with the frame stability and screen tearing for a pc that should run this game at 300+fps easily and what is causing the framerate instability. Prefer a response from a Riot Member, but, comm. input is appreciated.