Which OS are you on? Win 10? Did you upgrade from Win 7? On my current Dell, awhile back, I tried upgrading to Win 10 (from Win 7). Computer would seem to run fine for awhile, then would get a BSOD randomly. I finally pinpointed the cause as a graphics chip on the onboard PC not compatible with Win 10, and thus the crash. Not saying your problem is the same, but if you upgraded from Win 7 to 10, might be something to consider.
I still suggest you use software to burn and ISO to a LiveCD (or to bootable USB if that's easier for you) and use the LiveCD to just browse for an hour or two. If that works without freezing, I'm betting OS related and not hardware. As the monitoring you've done doesn't seem like a heat issue.
Here you go, you can download the current iso (and burn the iso to CD then just browse for a few hours and see what happens:
JustBrowsing LiveCD :: Home
Here is link to the current iso:
justbrowsing_20150220.iso