I took the time to read the whole way through and caught the part about a strange embouchure. First off, if you are playing on too much upper lip that explains your endurance problem. After a lesson with Lynn Nicholson, he fixed my similar problem. Over the years my embouchure had crept upward to about 2/3 upper lip and 1/3 lower lip. I was unaware of the move. Then I began having endurance issues. If the lips are not centered they take a lot of fast (loud) air to move, and because your upper lip is so large and heavy, it gets tired because of the excessive tension needed to sustain the air flow and vibrate. Your airstream hits the sidewall of the cup, and that backs things up even more, requiring more brute force to sustain. So when your chops are not centered you must work very hard to compensate for the bad habit. At that point very little progress can be made. Go and get just the rim of a mouthpiece. I had a machinist friend of mine cut off one from an old mouthpiece I had. Then look in the mirror and the chops should be at about the middle. Learn to play this way and things will get better. Practicing something wrong, only insures you will continue to play it wrong. There is no amount of overbite I have ever seen that would make the kind of compensation you describe necessary or wise.