if you have customs showing up, you have TU4 in place. you should also see it as Package Name “Rock Band 3 Title Update #4” in the RBtoUSB tool (same place you load all your customs). if you are missing a few, it means there are probably song id conflicts (which happens a bit). there are many threads talking about songs not showing up and fixing conflicting ids. it’s a bit technical, but a quick search should put you in the right direction. enjoy customs and welcome!
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!