GTX 1080 TI, Ryzen 7 1700x, 32gb ram 3200mhz - Low FPS in League

Hello I just recently bought a new PC and a new 144hz monitor. Been testing this new setup on League but my FPS is very unstable and does not even manage to stay on 144. I play with G sync on, V sync off, FPS cap on 144 and I usually get around 90-130 fps with occasional spikes down to 76. Also tried setting my monitor hz to 60 and the fps cap to 60 in game. Even then, then fps wouldn't be stable but it would go from 56 to 60 fps. One of my friends who also has a gtx 1080ti gets up to 300-400 fps and stable 144 fps. So am I doing something wrong? I tried reinstalling the drivers, reinstalling League and I did a few benchmarks on Firestrike (around 18600 score). Any help is appreciated!
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