Slow new-built computer, hight system interrupts

Oct 7, 2018
Hi Everyone, Ive built a pc recently, but something is not okay.. I tried almost all troubleshooting from youtube, without success. So I would appreciate all kind of suggestions :)
specs: MB: asus z370i, cpu: intel i5-8600k, gpu: asus gtx1080, ram: gskill 2x8gb 3600mhy ddr4, psu: bequiet sfx-l 600w, nzxt kraken x42, phanteks shift
Problems that Ive noticed:
-aprrox 5-10 minutes after start, everything gets really slow, and cpu usage will increase due to system interrupts (restart solve this issue temporarily)
-sometimes it connects to my regular wifi, but sometimes it acts like as a new connection and I have to do it manually
-mostly Im using it for CAD apps, which also gets really slow but thats the same during games. The fps graph looks like a saw tooth or gets really low. far cry 5 with low settings but on an ultra wide screen (3440x1440) around 10fps. But with lower resolution the fps is the same... and also on ultra settings so I hope thats not normal:O temps are great, gpu max around 70celsius, and cpu around 55c.
As you may see, im not an expert with computers.. should I ask for professional help somewhere or do you have any suggestion to try?
Thanks a lot in advance:)
here is a benchmark test:
Hope you can open it, but the main issue is related to GPU as it is performing way below expectations.


I asked about the GPU because there any many counterfeit (fake) devices on the market these days. Does the application GPU-Z identify the GPU properly?