The main plan for this style of tunnel is more of an Express way. Think like driving to someplace but the freeway goes through a large city (LA, San Deigo, San Francisco, etc) and you don't want to stop because you are just passing through to get to your location on the other side. You have to...
I have the s8 plus and I use bxactions. You can turn it off, Set an app or a function. I have it as a flashlight button. Makes outside working at night easy.
Edit: Also no root
For the cpu I use prime 95 for a few hours when I overclock. Here is a link to a short write up about stress testing.http://www.pcworld.com/article/2028882/keep-it-stable-stupid-how-to-stress-test-your-pc-hardware.html Another option If you really think that it is software is to change the boot...
Do you happen to have a spare PSU laying around or possible can borrow someones? I know that a bad power supply has caused random restarts for me before after upgrading a graphics card. Since you just added the graphics card a few weeks ago and that has over doubled your total system peak power...