I had this problem with random crashes. Read through all your past posts and figured I Best Buy me a new logic board. Got the board and opened up the guide to start the tear down. I got my matchbook pro 15” 2.3 dual graphic 16 gm ram all taken apart to realize I had accidentally ordered a logic board with integrated graphics. Frustrated I put the whole computer in the closet and decided to give it a break. The more I thought about it I realized one major step in replacing the board is to remove the thermal paste clean it up real well, and apply new paste. The paste on the old board was dry and cracked. So because I needed to get back to work and was tired of ordering parts, I cleaned it up, put the paste on and installed the old board. I have never had a problem since. I believe the machine is shutting down because it is overheating, it has a built in safeguard to stop it from becoming damaged. But with dry paste the heat can’t displace properly causing it to overheat. I think that is why on a cool start it would certainly last me longer, but in the end I could tell it was overheating, but buy no means would I believe the board was bad as the computer always returned to good working condition once it cooled. Anyhow, I hope this saves someone a lot of hassle.. Good Luck.