I have a late 2013 retina MacBook Pro that have served me well for years. A few days ago I installed the MacOS Sierra GM but after a few minutes of use my Mac without warning turned itself off. I was sure it was because if the Beta and I did a new clean install of El Capitan that used to work without issues. However the sudden shutdowns still occur! I'ved tried to reset SMC, run diagnostics (everything fine) and use disk utility but my Mac seems all fine. When my computer shuts off it goes black with lights still in the keyboard for 3-10 seconds until completely shut down. What can this issue be?