league of legends fps stuttering low performance r9-270x

I play on medium settings, no shadows, full hd resolution. It appeared randomly, not soon after a driver update or anything, just all of a sudden one game it started doing this. I've tried lots of stuff, by far nothing fixing it. I don't know why, but my gpu's frequency while i'm in game is 1000mhz, when the clock is 1120. I don't really play any other games, i tried cs:go and there were stutters that were similar but they go away after awhile. I've done chkdsk process on all of my drives, i tried the latest catalyst amd driver, tried reinstalling the game, tried repairing the client, tried playing on very low settings, i have msi afterburner to look at my gpu temperatures while ingame and cpu load and temperature too. I did furmark test. Temperatures seem fine.. If anything it seems like the gpu is too little loaded and it sometimes goes down to 450/300 mhz which sometimes causes the fps stuttering. A little deeper of what the fps stuttering is like: the screen freezes for parts of the second, it's really minor but when it's often it can be very frustrating.. In some games it goes hardcore by freezing like 10 times more often than the usual which is just so bad.. The hardcore freezing i think starts after having played like all day, so basically by the end of the day. If i cap the fps to lets say 144, the gpu frequency goes down to 450mhz solid and sometimes to even 300mhz and when i do cap it the game becomes very not smooth, even tho the fps counter says 144.. If i cap it to 60fps it stays solid at 300mhz and the lagging is so bad it's like frame skipping and i see those kind of lines that v-sync prevents. So it's very weird. Today I tested if i would get the same issue using my integrated hd 4600 graphics and it was gone. So the problem is definitely caused by the gpu. What I haven't tried is reinstalling my windows and cleaning the pc (I'll clean it tomorrow) and I guess changing the thermal paste. I saw on an amd forum someone with similar problems and they told him to reinstall his windows and get all the latest updates, do you guys think it's good to get all windows 7 updates? I feel like they'll screw me over more than help me, plus the only thing I think they do is update the security. Please let me know of any possible solutions and if need more info to help understand the problem better, thank you.
cpu: i5-4670
ram: 8gb
gpu: r9-270x
driver: 16.10.2 hotfix