x17 R2, Strange (overheating?) shutdown issue

I just had this month-old x17 R2 laptop repaired by a technician (new motherboard installed) due to a faulty adapter frying the old motherboard - it now operates without almost any issue, except a very strange shutdown problem. It can run low-resource operations just fine, but within minutes to seconds of running anything that requires medium-high resource costs (such as running the menu screen of a steam game) it shuts down. The shutdown is the normal black screen with the words "shutting down", and it's able to be turned right back on afterwards with all processes closed. 

What's strange is that, not only has it never had overheating issues before, but running both SpeedFan and the Alienware Command Center to monitor internal temperatures shows nothing overheating at all; the highest temperature when it shutdown was the graphics card at 68C°. The fans spin up just fine with relation to the amount of heat everything is generating, and audibly turn on before it shuts down. All 4 fans passed all tests I tried, and they spit out a lot of heat.

As a side note, the Alienware Command Center is unable to control the fan speed at all with its thermal settings. I don't think this is too relevant as the fans operate just fine anyway, and it seems like this is a common problem based on a simple google search. 

Edit: As another small side note, I've occasionally been getting the BSOD "RERENCE_BY_POINTER" error. It occurs randomly and infrequently, but it's done it multiple times now.