I've been playing trumpet for 7 years now (I'm a sophomore in high school, so it's really only been 3 years of actual practice and work), and although I am gaining chop strength in many ways, there's always one thing that has been a problem for me: taking breaks. Even if I only play for a few minutes, if I take a 15+ minute break my chops are NEVER where they were when I began. This happens during gigs (I'll be playing well the first set, then there's a break, and I can't play at all the second set, even if I warm up again), and, most inconveniently, at auditions (I warm up for 10 or so minutes, then wait half an hour to be called into the audition room and can't play, even if I warm up again). Is this normal? I've seen some older people have no problem with this (only slightly older, by 2-3 years), it seems to be only me. If so, how can I fix this? Is it related to endurance in any way?