For a long time I've hit a wall at E over high C in my range. In fact some days I can't even hit it, so I consider D to be my highest usable note. When practicing I can move up to the Eb but the E is very elusive. I have been experimenting lately, trying to make sure my embouchure is correct, air support, etc. It just seems like when I get to that E my lips stop buzzing, and I can't figure out why. I've tried taking the trumpet away from my lips while playing various notes, and above the Eb they just aren't vibrating. I should also note that it's very difficult for me to lip buzz w/o a mouthpiece. I've seen videos of guys buzzing all over the place, high and low. I just can't seem to do it. What do you guys think?