The regular troubleshooting goes like:
- Check out mods, and solo game;
- Check out the .Net framework and DX versions, and video driver update;
If everything checks out (it still have problems with no mods and updated drivers), you might have something else interfering with the game.
Mostly it happens when you using multiple screens, or third part softwares to manage memory, video or streaming.
In any case, try to run the game with NOTHING ELSE running, with updated drivers and no mods. If it is still crashing, you might have a problem with the System itself.
Remember that having specs “way above” might be a problem too if you running Ultra. The specs are designed to run minimal in “minimal” and recommended in “medium”. To run ultra you do need a lot more than the recommended, and in Isle of Siptah, much more yet, because it uses the new features in UE for lighting and extrusion of 2d textures.