What MipMap fix does is force away the upgrade/downgrade system, and simply makes the game load the highest resolution texture you allow via settings to load in immediately. 2 is the lowest, like low and medium, 1 is High, 0 is ultra, and -1 is MipMap fix. The MipMap option this new launcher has has -1, 0, 1, and 2. One of the tweaks this launcher has is MipMap options.

This replaces your Default Launcher for Fallout 4, and it has many many settings to further tweak your game via the launcher instead of INI file changes, and fine tune the settings that the default launcher has. The best solution is the Fallout 4 Config tool by Bilago The easiest way to fix it short term is to restart your game. What happens is the upgrading wonks out and you either get shitty low resolution textures on an item and it either gives you what is called 'pop in' when you are finally up close on it, or you get rainbow textures, because the system wonked out and is stuck between your highest graphical setting and the process of upgrading/downgrading. So this is not a file problem, this is not a CPU or GPU problem, this is a coding issue IN the game itself. This doesn't always work like it is supposed to.

*The heat you are experiencing is because your GPU is being worked like a 2 dollar prostitute on half price night because its having to do a lot more work in a smaller allotment of time because of s*** coding.* MipMap functions like this, say you are 300m from an object, its too far to require ultra texture mapping, so it registers them as say medium, as you advance, it periodically upgrades the texture map quality of the target, so now you are 250m from it and it upgrades to High from Medium, it stays at High until you reach 175m, then it upgrades to Ultra, depending on how far you have you settings at it may not even hit Ultra until you are MUCH closer.

Fallout 4 rainbow textures fix