Power Supply Possible Problem (sudden shut down) FINALLY SOLVED

Good chance the problem is your PSU again. Unfortunately the TR2 series were not very good. The linked list has the TR2 RX series listed as a Tier 5 (Replace immediately, dangerous) product. This list was last updated 12/2014.
https://community.newegg.com/eggxpert/computer_hardware/f/135081/t/45344.aspx
It used to be tier 5 in Toms list also (http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html) but has been dropped from the list. You can check this list and see which current ThermalTake models are decent.
If you replace that PSU I recommend, especially with your specifications, that you choose something from Tier 1 or 2 on the Tom's Hardware list.

Your welcome. The P2 versions of EVGA psu's are well built and should last a long time.
If that doesn't solve the problem please repost or drop me a p.m. with link to any new thread.
Have a great weekend !

Chasing memory problems is usually really time consuming and frustrating. I just looked at your motherboard (this is it, correct; http://www.newegg.com/Product/Product.aspx?Item=N82E16813128514
http://www.gigabyte.us/products/product-page.aspx?pid=4672#sp ) and it is not certified for DDR3 2400. That could be the problem.
Go ahead and try your 1333 RAM, see if that doesn't solve it. You could also go into the UEFI/BIOS and underclock your current ram to, say, 1600. You wouldn't see any real world difference.
Keep us posted, especially if the 1333 RAM solves the problem.

I guess it could be too low, but don't think so. Try the other 4 sticks and see what happens; I make this suggestion because testing RAM becomes a really laborious task and it the pc runs with the older 4 sticks you have solved the problem.
There are other things that can be causing the problem, but try to work on one thing at a time so that you know what the problem was.. BTW, are you still on Windows 7?
P.S. Edit: Since this is NOT solved I 'unselected' the best answer; hopefully others will read and post.

If you go to the Windows 10 forum, there is a 'sticky' at the top to help you make an ISO (either disc or flash drive) so that you can later do a clean install of W10. Someone also indicated there is a way to do the ISO image install without losing files. When you decide or it gets to the point of reinstalling 10, then you can use the image to do so. It's a good tutorial.

Have you checked in "Event Viewer" to see if there are any clues therein (in the start window type 'event viewer' and the first entry should be the program-rt. click and open as administrator). When my wife's MSI board failed I found only two 'critical event' entries out of about 200 that pointed directly to the mobo: Both indicated a shutdown or error with the AMD Northbridge. All the rest of the critical errors appeared random and different. New mobo solved the problem (but I also upgraded the CPU and ram). As you are doing, I checked everything: replaced RAM, replaced PSU (a good thing as the one in her system was getting old); tried a diff. processor; ran memtest for hours and hours (never found anything, but testing the RAM in another similar system found two suspicious sticks that would not allow boot, replaced under warranty).
I really don't think it is your W7 install causing this; OS problems often/usually show up as bsod's or just plain failures to load or some programs just don't work correctly, as opposed to shutting down the PC.
You are doing a good job of troubleshooting; I guess it could be the video card and changing that is worth a try, but most of the time (though not always) a faulty video card will cause problems when under load such as gaming.
Have helped a couple people in the last two years where their problem ultimately was the CPU: So changing that is a good plan, and even a call to AMD might be in order. Processors are usually so dependable that we tend to think they never fail, but they do.
And you are right: if the video card change and cpu change doesn't solve the problem, then it will come down to the mobo. One of the things that can happen is the mobo circuit protection is "discovering" or "detecting" a power surge or drop and shutting down the PC. From other threads and forums, this action can pop-up a notice of the detection, and there should be something in the event viewer. Sometimes these shut downs are for real, but several of the the threads I have read, here and at another forum, revealed that the circuit protection on the mobo was defective or too sensitive.
Sorry for the long answer, but am heading off to appointments and work, won't be back on for some time. Please continue to keep us posted.

Sorry I have been absent for so long, but it has been a really difficult and busy couple of months, and as of right now it doesn't look like much change in that; but had a few minutes to look at the thread again so here I am.
Nice job of trouble shooting and patience; I am truly happy that you were able to find the problem. This is the second or third thread in the last ~3yrs. where the problem was the CPU. The one I spent the most time on was also an AMD processor. I am not saying they are bad, it is all that I run on my computers at this time ('cept my laptop) and never had an issue with them, but I will remember these threads when I next build a PC.
As you know CPU's very rarely go bad (remember that there are millions and millions of them out there being used every day) so they are, as you found out, rather difficult and time consuming to track down.
You shouldn't have any problem with AMD; After telling them (if they even ask) how you determined it was the CPU I am sure they will help you out. I have dealt with them twice and they were quite helpful.
My apologies for the long post, and again - Congratulations on solving the problem.

THANKS! Still don't have much time to spend here, but it is good to be back.

Glad to hear it wasn't the CPU; I was starting to get a little worried about AMD.
How did the knee surgery go? My best wishes for a speedy and successful recovery. Much as I hate Physical Therapy (also know as Physical Terrorist) it is my understanding that the P.T. is much more important to complete and follow-through with when the knee has been operated on: Trust me, I know Lots of people who have had knee surgery and they have all told me this - especially the ones who opted out of PT and their knee never really fully recovered.
Hang in there, it will bet better.
And now, at least, you don't have to worry about the freaking PC acting up!
Happy Thanksgiving!