Every instrument offers certain challenges that are intrinsic to its mechanism and design. Practice Monster is easily angered by things he doesn't understand . . . like physics. In awkward keys, or uncomfortable parts of the horn, even a modest passage of music can create serious problems for the performer. Aside from the technical challenges, basic musicality is frequently compromised when our attention shifts to the distractions of technique.
I was lucky to attend a masterclass given by legendary flutist (and practice master), Trevor Wye. He addressed this issue with an approach that I have come to think of as "right key, wrong key, right key." Simply put, move the passage into an easier key with the goal of performing it as musically as possible. Temporarily free from the added mechanical challenges, aim for perfection, and listen for details of phrasing that you may have missed before. After a brief session in the "wrong key," return to the original transposition. In my experience, the results are frequently instantaneous. Remember, listening is the most important musical technique of them all. The best musicians can push the limits of their fingers and their ears at the same time (and this is more difficult than it seems).
Besides the obvious concept of moving a half-step away, or into a less complex key signature, try playing in a different register. If the passage crosses the break, try moving it into a key that stays in one register. It can also be musically useful to shift only portions of the overall passage, to keep everything in the same octave, or register. Be creative while you work, and the monster will be soothed.