I am sure there has been posts of this topic. I have been playing the trumpet for 28 years and still have difficulty playing in the upper register. I tend to tense up and just can't relax. It doesn't help that my teeth aren't the greatest, they're crooked and a few are broken. I am way too terrified to go to the dentist and probably will never go again because of a childhood trauma but anyway I can hit high notes but it is a struggle and I usually have to really press the mouthpiece against my lips really hard. I know this is no good but that seems to be the only way I can get out any high notes.