I broke a skill wall recently, so this might help.
For speed, 4K is primarily muscular (your issues are not psychological from what I've seen). If you plateau you're probably not using a muscle right or something like that. Your best bet is to use a more optimal technique (or at least a technique that gives better results than before). There are obviously no "perfect" technique, so you have to fiddle around with your posture. People generally play with their wrists raised, which gives significantly better one hand trilling speed but issues with jacking as they have less leverage on their wrists. People play with their wrists planted, which gives better jacking ability and but you require significantly more tension to hit one hand trills. I've recently swapped for the former, managed to hit significantly faster streams and patterns that I need a very good day on to nail without warming up with a new technique.
Reading is a different thing altogether and I don't think that's your issue. If your reading ability isn't improving at all you're probably not focusing at the right area. Try reading with less space with Hidden, Flashlight, or open up Task Manager and cover up some of the screen. You could also increase your speedmod if you focus more on the spaces between notes, or decrease your speedmod if you focus more on the overall direction of the notes.
Also don't think about breaking your skill wall. You're adding unnecessary stress to yourself.