Just recently, whenever I start mining my PC slows to a crawl. I have been mining for a few months and using my PC (with a 1080 ti) perfectly fine at maximum intensity. Now even if I set it to intensity 1 it still slows down my PC significantly (I can tell because when on youtube the FPS of the video drops significantly). I have been trying to find the bottleneck but I can’t find anything. My CPUs utilization is low, my RAM and VRAM is no where close to being filled and at intensity 1 my GPU utilization is sitting around 90%. It’s possibly got something to do with firefox because I switched from Chrome to Firefox at the same time this started happening, but that would be bizarre, especially since it’s slowing the entire system and not just the browser.
Also, I’m using Gentoo Linux and the EWBF CUDA miner. Any help will be appreciated 
is your card overclocked? is gpu connected to monitor?
how old is your board and cpu? (brand and models)
My card is factory overclocked, the temps usually hover around 70 C when mining. The GPU is connected to my monitor, I also occasionally do other stuff with my GPU (I game on it and like to do other things on it sometimes such as contributing to projects like World Community Grid occasionally. I have also once video edited with it and I plan on learning how to use CUDA and OpenGL with python soon). My CPU is an I7 6700k not overclocked and my motherboard is an ASUS ROG Maximus VIII Hero Alpha.
Me and my roommate both mine on our personal computers and we experience the same thing you mentioned above. I just kinda assumed this was normal behavior. Although If someone does find a fix that would be great! I noticed that if I drop my resolution from 1080p to like 360p the video doesn’t lag but then it looks like a potato.