I also regularly experience this issue. It seems to be an issue with the algorithm in the game for getting data to make mipmaps from. Mipmaps are smaller versions of your texture which the game uses for rendering at different distances. This is why close up you (almost) never see this issue, and it is generally very affected by camera angle/distance.
You can reduce the issue by making sure that all your UV islands have nice big like-colored dead zones/borders around them. I didn't know this early on and have paid the price.
The game's mipmaps are 1/2 size at each 'level'. So, at the first level, your UV island border pixels are blended with 1 pixel (from the original sized image) from across the border. At the 2nd level, 2 pixels, 3rd level 4 pixels, 4th level 8 pixels, 5th level 16 pixels. It's a bit more complicated than that, but that is kind of the general idea. You have to balance the size of your border areas with the level at which the mipmap has so little detail it doesn't really matter. Like, a 2K texture will have 11 mipmap levels, which would need UV island borders of 1024px to be "perfect" at the last level ... but that last level is only 1 pixel, so what detail would you really be trying to preserve with that?
For me, personally, I find 16px for 2K textures to be a good balance.
A reason why you see this less in default textures is that they use the TPC format, which includes precomputed mipmap images (for which, presumably, they took care to make sure the mipmaps came out with good visual characteristics). TGA images don't have mipmaps, so they are generated by your video card (there is an OpenGL function that does this), which is also why there is some variance w/ different cards/drivers/etc. Seems like driver-level AA settings would help too, but in-game AA settings don't seem to affect the issue.
In an ideal world, the mipmap generation would use UV mapping to refrain from using pixels from outside the UV islands, but that is not 2003 tech
My understanding for why this issue never really goes away is that the game seems to maybe use black pixels when a mipmap is blending with pixels outside the border of the image. That is just a theory though.