Hi, after all the help you've given me, I've solved the problem of the high notes on my new mouthpiece. However, there is another problem. While I can play my range again, I can only do this for about ten minutes after I am warmed up. After that, I begin losing range and tone. My question is: how do I build up the endurance? I can't practice anymore than twenty minutes because I cannot play well anymore at that time. How do I increase the limit my lips can take of stress? Any exercises, practice techniques, etc.? Thanks for the help!!!