I was on my way to making a "high-res" pack *making everything in the LFS DDS folder 2x's it's size, and seems like one of the files that I enlarged, puts this black background behind it. It's a tree file, and it seems to be this tree in particular (few of them around the track) It's the tree to the left of the Dunlop on Blackwood if you doing the track forward. Check the pic if you know which exact file it is. I've tried going through most or all of them to see if there's some comparison in the files, but can't seem to narrow it down to one file.

you cant just enlarge every texture, it'll only make the quality worse..

Making the textures twice the size will have absolutely no effect whatsoever. Textures will not be more detailed by just erlarging them. I made a high res asphalt pack for BW but I was not only making them 2x size but also adding some filters in photoshop and mixing with other textures to have more detailed look.