I was getting random CTD's (without any error messages in dxdiag or event viewer) anywhere from 5mins to 2hrs of gaming, and tried EVERYTHING to fix it. Now, I'm not sure if you overclock your CPU, but I have an i5 6600k running at 4.5ghz. My system is 100% stable. Runs Prime95 v27.9 24hrs, memtest86+ 24hrs, all other games (ex The Witcher 3, BF4) wouldn't crash so I didn't even think it could be CPU related? I never tried going back to stock speeds on my CPU, but it looks like it ended up being the culprit. Even if you don't overclock, this still might be a solution due to how default voltages work and motherboard power saving features.

I started noticing that the random crashes would happen in less CPU intensive areas, and that got me thinking that it might have to do with my voltages (as I overclock with adaptive voltage). I decided to try changing to adaptive + offest voltage and added +0.010 to my offset and now I haven't had a crash in a week. I did originally try +0.020 and worked my way down to +0.005, but it would crash again, so I settled on +0.010. I've played probably 4-5hrs a night (and my overclock is still on 4.5ghz) without a single CTD.

In my case, my CPU was crashing the game in less intensive areas because it would down volt due to less usage and power saving and this would cause instability in Fallout 4. Never happened in any other game or program except this one.

Now, I'm not saying that this might be the cause of your problem, but if you run power saving features in your bios (which you most likely are, especially if you don't overclock) I suggest adding an offset voltage starting at +0.050 and seeing if you still crash (if you're trying this on an overclocked CPU, then you should know if adding +0.050 will still be safe and if your borderline try starting lower). If you don't crash, then work your way down in 0.005 increments until unstable again, then put back to your last setting. I say start at +0.050 because what worked for me may not work for you, every CPU and motherboard is different. If +0.050 doesn't work, then anything higher probably won't either.

P.S. If you decide to give this a go, but you know nothing about your bios and voltages, don't try any changes until you read up on overclocking and the different types of voltage settings in your bios. You may cause serious damage if you don't know what you're doing. Also, if this doesn't work for you I'm sorry I understand your frustrations with all these CTD's, just wanted to post what worked for me.

tl;dr - If you're running power savings features via your bios (which you most likely are), try adding an offest voltage of up to +0.050 to your CPU. If this doesn't work and Fallout 4 still CTD's, anything higher probably won't work either. Did for me tho.