CTDs and Freezing while playing Fallout 4

[Bad Demographic]

Bob's pc has a big problem with frequent lockups and ctd's while playing Fallout 4. I've tried a lot of "remedies" and sometimes he can play for a few hours before the problems show up again.

System info:
OS = Windows 7 64-bit pro
Mobo EVGA P67 FTW
CPU = Intel i5 2500 3.3 Gig Socket
PSU = 650 w.
RAM = 16 GHz (4 4GHz sticks) DDR3
Graphics card: Gigabyte GeForce GTX 950 OC 2GB GDDR5 (PCI-Express 3.0)

The RAM and graphics card are new. The mobo is from 2011.

What I've tried:
cleared the old video drivers (old card was GeForce GTX 460, or something like that), installed new video drivers (using GeForce Experience)
dl'd updated bios and audio drivers
underclocked the video card a little (I don't recall the settings now)

Bob thinks the problems happen most when he's building stuff for settlements or modifying weapons/armor, but it also happens sometimes just minutes into a game or during a fight. The problems really occur pretty randomly.

One thing I'm wondering about is if having a PCI-Express 3.0 card in a PCI-Express 2.0 slot (the mobo is too old to have a 3.0 slot) could be part of the problem?
Any ideas? Things to try?
Does anybody here have a similar problem?

[Isgrimnur]

memtest to scan his ram, scandsk to make sure the hard drive isn't going bad.

[Bad Demographic]

Ran scandsk and all was okay. Will try memtest (when I get a real break from scaping wallpaper).

[Bad Demographic]

Ran memtest. RAM is good.

[Giles Habibula]

All other newer games run fine? This is only with Fallout 4?

[Bad Demographic]

All other newer games run fine? This is only with Fallout 4?

Fallout 4 is pretty much his only newer game. I'll ask him to check Civ 5 and Borderlands 2 - those are his next "newer" games.

[TheMix]

I'm not sure I can help. I'm currently running an AMD card.

I get crashes. Sorta. Except not to the desktop. Instead, my pc (presumably) keeps running along. At least, I can hear the music. However, my monitor shuts off. Apparently my video drivers shut down. The only way that I can get going again is to reboot the PC.

I was able to determine that it only happens when it's raining. So now I do my best to avoid the rain.

Other than that, you can try googling. There are lots of threads for Nvidia issues. I just don't know whether his issue will be addressed.

Oh, I do occasionally run into the "shuts down 3 seconds after starting" bug. I think it's a permissions on one of my .ini files. Either one is read only when it shouldn't be, or the other way around. The only way that I've figured out how to deal with that one is to re-validate my game files. Usually it will download 2-3 files again.

[Victoria Raverna]

Have you tried "Verify integrity of game cache"?

[Bad Demographic]

Have you tried "Verify integrity of game cache"?

I'm pretty sure we have, but it won't hurt to try again.