Guess what, that was the problem !
I removed the cooling fan and heat sink
Completely cleaned all the dust from it and the fan and put a new layer of
heat conducting paste between the heat sink and the CPU.
Before, I could only get a little over 2 hours computer run time and it
would just shut down (this same thing occurred 5 times doing the same thing)
like someone yanked the plug out of the wall.
Now I ran my computer 21 hrs straight - running the most CPU intensive
software I know of for 20 of the 21 hrs with no problem
So I'm pretty sure I got it licked !
By the way before I did the cleaning thing, it only took an hr for my bios
to warn me that I hit 122 deg F.
My shutdown temp is 158 deg F - pretty easy to imagine it hitting that temp
when in an hr it goes from 95 deg F to 122 deg F.