15" MacBook Pro (early 2013; Retina) locking up hard and autorebooting.

Hello.

I have an used 15" MacBook Pro (early 2013; Retina; 2.4 Ghz Intel Core
i7; 16 GB of RAM 1600 MHz DDR3; NVIDIA GeForce GT 650M 1 GB of VRAM; 250
GB SSD; Mac OS X v10.10.5 [Yosemite]) that is locking up hard and
autorebooting once in a while. It has been happening since summer 2015.
I think it is only happening when it is heavily used in the warm and hot
weathers (~80F degrees indoor for today's crash) like when I use 64-bit
Windows 7 EE SP1 VM in VMware Fusion. I can feel heat on the keyboard
case and from the keys so I assume it is heat related.

I did not have any problems when it was cold like in the 60-70F degrees
indoor. In the past, I have seen this happen. I even saw one time
showing a kernel panic on screen.

Is there a way to check with stress test (e.g, Prime95) like in Windows?
I checked with CheckMyApp and it shows both side fans spinning over 2K
RPMs. Even forcing 5K RPMs work loudly so the fans do work so I doubt it
is a fan issue.

Thank you in advance. 🙂