Hello PillarsStutterSufferer.
I have the exact same problem, periodic stutter every 30 sec or so .
Ive got this problem since release , day one.
Like you did , i tried many many things without succes (everything that you listed i did too) .
I made post about it , read online, a lot ppl actually suffer from this too, ive watched lets play on youtube and i can see stutter too.
I tested the game on 3 different pc , my desktop, gaming laptop and my brother's desktop with the exact same stutter on 3 different computer with different hardware and os.
After extensive testing I was able to find out that its related to your framerate and the amount of character you have in your party
If i play at 144 fps i will get stutter every 25 secs (i dont remember the exact number but its close to that)
If i play at 45 fps it get stutter every minute.
The frame time get a huge spike like 255 ms between 2 frame that cause the stutter.
when you remove one compagnon from your party , you gain about 25 seconds each time, so if you do a solo playthrough you will get periodic stutter around every 2mim if you play at 45 fps .
This will never be adressed, i get this with deadfire too, but the frametime spike happen every 3 min or 6 min so its more playable but still annoying.
The only way to fix this bug is on the programmer side. Its probably garbage colllection issue that cause the frame time spiking this way and the fact that it happen more often with high framerate is a proof of that.
(sry my english is not so good)