Gentlemen,
  Thanks for the swift replies!  Over the course of the next couple of days; I will re-install the 1080 then try both of your suggestions 
But please be patient, as I typically work evenings and I don't have a lot of time during the day before I have to go into work.  I actually took tonight off to devote some time
to hardware swapping...and my 2 cats just love to help!
Most appreciated!

Update:   While I still have my 970's installed, I thought that I would run Fire Strike so I could compare results from the 1080...
The results were disturbing:
EVGA GTX1080 SC :        16375/22855/11107/6782 : http://www.3dmark.com/3dm/13221262?  power limit @ 120 no other OC...reported Core Clock 2000Mhz ...temps never above 65C 
2x MSI GTX970 Gold Ed:  15992/23324/10975/5986 : http://www.3dmark.com/3dm/13418170?  power limit @110  my mild OC applied (+125 mem on both...+85/125 Core)
 
When I had looked at my 1080 scores before, I compared them to other scores with the same CPU (i7 2600k) and they seemed only slightly above mine http://www.3dmark.com/fs/8736591
 I had attributed my lower than 1080 review scores due to my aging CPU so I was too concerned.  
But why should 1080 graphics score be below my 970 SLI score? 
 
Next step: re-install the 1080 with applicable driver purge (DDU)
 
update before work:
GTX1080 Fire Strike Extreme (1440)  9621/10854/11052/4704
GTX1080 mem underclocked 500 (4010Mhz(....still CTD in Fallout 4....
 
update after work:
I found that its specific graphics setting in Fallout 4 that are causing the CTGs (some would say, "well of course!").
I am trying to narrow it down to which specific setting and thus better understand my issue.  
So far, I have successfully been able to play without a CTG :at 1440 with  a mix of High and Ultra settings (view distances maxed).  Shadows, Godrays, and Weapon Debris seem to be the issue.
In contrast, with my 970 SLI setup; I was able to play at mostly Ultra with Mods.  No crashes, but with framerate slow downs in Boston (which is normal for all). 

Hey Thumper I follow you from steam forum
I got two GTX1080 founder edition run in SLI for Surround config 5760x1080 without HB SLI bridge (yet).
And I also got CTD randomly from 20 minutes to few hours.
I did tried disable HBAO+ and Weapon debris and still got crash with out error.

Start a new game. Your save might be corrupt.
 
Yes, I am serious. I had this issue too.
 
Also, if you have any mods, remove them as well (just in case).

r2d2fd,
 
  My issues seem to be a combination of my Windows 7 install, my CPU/Memory, the new GTX1080 and Fallout 4.
 I  have played over 300 hours of Fallout 4 played at 1440 (with multiple Mods installed) on my 970 SLI system; with all setting on Ultra except Shadows Quality/Distance, Godrays and Weapon Debris (those were on High or Medium).  With the 970's I had some FPS slowdowns, but no CTD's even if EVERYTHING was maxed-out and my framerate was 60-40 (VSYNC enabled).
  With the GTX 1080, I have to play with almost the same settings, because if I go higher I get CTDs without errors messages.  You mentioned that you have experienced CTDs even after several hours of gameplay.
I may as well...even with 
Currently, there are no Mods installed and Fallout 4 has been completely re-downloaded and re-installed.
MSI Afterburner, does not seem to show any indicator for the crash-event...but I am far from an expert in its use.   On the other hand I am not a novice trouble-shooter either, I've been a Test Tech in the Semiconductor world for 20+ years...its what I do...its how I think.
  The only thing that has been suggested, that I haven't done, is to disable the Overclock on my CPU.  In order to change my BIOS settings I'll have to dig out a PS2 keyboard as my BIOS will not see a USB keyboard.
I have also thought about installing the 1080 in a friends computers and seeing the results.  But even if it performs without issue in his newly built computer, it doesn't help me with my computer.
Up to this point, I have had no other indicators that any other component in my system are at fault.

Thumper1958
 
  The only thing that has been suggested, that I haven't done, is to disable the Overclock on my CPU.  In order to change my BIOS settings I'll have to dig out a PS2 keyboard as my BIOS will not see a USB keyboard.
 

Use 'Debug' mode in the Nvidia Control Panel.
 
http://forums.evga.com/FindPost/2504606
 
See #3 in that post.

...update:
Using Afterburner: I set the Core Clock to -400 (this is below Nvidia default) and Mem to -502.....seemed to take a little longer, but still CTD in Fallout 4
Reset GPU clocks...
Finally got into Mobo BIOS...set settings to default (i.e. no CPU OC...confirmed with CPUZ).....still have CTD in Fallout 4...seemed about the same amout of gameplay to produce the CTD.
With the 1080, I've played Crysis 3 without issue for ~1.5hrs, but I haven't played Witcher 3 for more than 30mins, so I need to play Witcher 3 for a longer time period to actually confirm that it really
has no issues.
I also need to find a Benchmark or game that stresses the 1080 as much as possible so that I can further confirm that its Fallout 4 that is the issue, and not my 1080.
 
As I mentioned in my first post; I've already let Heaven run for over an hour without any evidence of video corruption or driver failure. Temps never went higher than the mid-60s
 
Benchmark or game suggestions?   Is Furmark still sanctioned?  Is there any way to test "all" of the VRAM?  I should probably run Firemark Ultra and see if I have any issues....
 

Thumper1958
EVGATech_RayH
I understand that my post was long and you may have missed it:  the current install of Fallout 4 is un-modded.  

Sorry about that, I did miss that.
I recommend an extended test of Unigine Heaven or Valley on the card.

Thumper1958
Is Furmark still sanctioned?  Is there any way to test "all" of the VRAM?  

Yes to first question. No to second question.

...latest update:
Ran Fire Strike Ultra without issue (Core @ 1962 ) and Fire Strike Stress Test passed ...97.8% stable....
 
...this morning's update...and an interesting twist....
As I had my 970's just lying around, I thought I might try installing one as a dedicated Physx card...and the results: no CTD in Fallout 4 (so far).  I have Ugrids now set to 7 (default is 5) and I ran around all over Boston with a full-auto weapon in God Mode, aggro-ing everything I ran into and no CTD for a good 30mins!
Again, does this point to Fallout 4 or my GTX 1080 SC?