How old is your psu? What happens when you underclock the core & memory to max negative?

I have 2 GTX 780 Ti classified cards with SLI bridge mounted in full sized tower case
 
I had the exact same problems when playing high demand games (ie. Fallout 4, assassins creed Origins.)  They were both played in ultra mode with the card in default mode.  The card would reach temps of 80 degrees C. and while fail times were different it would always crash.
 
Ran tests, performed updates, no change
I opened the case to do visual check.
Rear fan blade had failed and was sitting on PSU.
 
Removed failed card and am running on remaining graphics card.
 
Waiting to hear from EVGA about the matter.
 
ASUS Prime H270-Pro MB
i5 -7400 CPU @ 3GHz
16 GB Ram
windows 7 64 bit OS
850 W  modular X4 PSU
 NVMe Samsung SSD 960 drive 500MB c: drive
ST1000DM003-9yn162 !TB HDD e: drive
 
                           
 
    

Mrtechnologist2u
Solved my fan issue!
 
The blade just lifted out. Actually fell out while running.
 
I just unscrewed the defective fan motor assembly by removing the 3 screws
I flipped over the fan motor and carefully removed the sticker covering the back of the motor.
A small thin white washer stuck to the tape.  I removed it and cleaned it and put it aside.
The bearing was removed  by just gently pushing on it.  I cleaned the old crappy grease/oil on the bearing, spring and fan shaft.
Lubricated all with a drop of fine, low friction oil.  I used oil from my turntable kit.  Sewing machine oil should work as well. 
Do not clean with solvent like WD 40 without oiling afterwards.  Solvent cleaners have little or NO lubrication qualities.
Especially at the  speeds these fans run at!
 
Replace the clean and oiled spring and bearing on the fan shaft.  Insert into the fan motor assembly.  Now place the small white washer on the end of the shaft.
Using 2 small flat screwdrivers push the washer down over the shaft until it seats in the thin groove on the end of the fan blade shaft.
Replace the sticker over the back of the fan assembly. 
re-install the fan assembly and secure with the 3 screws
 
Works like a charm now.
 
I would think this would be good thing to do for any fan that is sticking or even for preventative care.
You would not believe how thick and hard old oil can get!
 

A very interesting solution so thanks for sharing

Respectfully:  My concern is that if the grease used for the fan is so correct why do I read about so many fanoverheating  issues.
regarding evga cards? The grease in my case was caked on
 
 
The GTX 780 Ti Dual Bios CLASSIFIED card (x2 in my case)  is a "WARM" card when running full out!)
 
ie:  Fan blades sticking
      fan blade separation
      card overheating and blade assembly just pulls out.
The only response I had from EVGA was they don't offer any support for fan issues unless the card is in warranty.
 
You would have thought they could have offered a fix for me other buy another card!
 
These cards were/are an expensive card to buy, and to replace them even more so.  I was disappointed in their response.
If the washers are an issue, replacements would not be an expensive item to offer as spares or replacement even if replacement fans are not available.
Perhaps even offer little tiny appropriate packets of grease or oil to do preventative  maintenance.
I could even fabricate my own retaining washer, out PE or even brass shim stock, if they had given me the dimensions.
 
This was an easy fix taking 5 minutes of my time after not getting any help from EVGA.  Anyone with a jeweler's screwdriver set and a pair of tweezers should be able to do this.
 
Please note: I know I am venting a bit.  Other than this time, I have been very pleased with EVGA and their product and support.  What bothered me so much is how little it would have required from them to assist in this problem.  There is only 1 reason the fan blade can come out of the assembly!