Lags and screen tearing with a gtx 1070, i5 8600k and 16gb ddr4 ram

Im having performance issues since like last preseason, and its pissing me off, because my pc is supposed to be overkill for league, and it still runs like shit. Sometimes it jumps down to 70-80 from 144, and with a 144hz monitor this makes my eyes bleed, and sometimes my screen just stops for a second and then goes on again. There are games where my auto attacks lag mid animation and dont finish, making me miss a cannon (lul). It pisses me off because none of my friends seem to have this problem, and I tried so many things already with no results whatsoever. I tried reinstalling windows, every possible driver, reinstalling league, repairing the client, I even tried it out with a different cpu and the problem still holds up. If anyone has any idea what could might help I'd be more than happy to read it.
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