I'm going to approach this a bit differently than some others have, because I see a different issue here, although I'll echo what others have said about excessive pressure. I've highlighted what I feel to be relevant parts of this post. What trumpet are you using? The reason I ask is because I've played trumpets where the E above high C just doesn't want to slot. I can drill the Eb and F around it, but the E doesn't want to slot or center - it just squirrels all around. I've also had an interesting kind of thing in that register where sometimes I can punch the E, but then the F doesn't want to slot. If the F is slotting, then the E doesn't seem to want to center. Keep in mind, for me that's creeping toward the top of what I can hit - notice I didn't say "play" - my usable gig range ends at about Eb. So, a couple of questions: 1.) What trumpet are you using? 2.) Have you tried other valve combinations to get the E to slot such as 1&2, or 3rd valve? 3.) Have you tried other people's trumpet and had the same issue? 4.) Have you tried other people's mouthpieces to see if the issue is better or worse with them? I don't think a different mouthpiece is going to be the answer here. Reducing pressure will certainly help you to find the center of the note, but if the horn has a problem slotting it, that's a different issue altogether. There are going to be some who read my post who want to naysay - they'll run this whole thing back to pressure, but if you're getting everything up to A, I don't see pressure as being the overriding concern. If pressure was the full problem, you'd get cut off long before you got to G or A. That's just this guys opinion though, and you know what they say about opinions.