One of my university students (a trombone player) was experiencng this same tightness in the upper register. Hers began around Eb above the staff. Fs got really tight sounding, and she just could not hold a full forte dynamic for very long. So, I used the "Taw" thing. She thought I was nuts at first, but it really opened up her higher register in a matter of minutes. It is still a bit rough around the edges and needs cleaning and focusing, but it is definitely a step in the right direction. Thanks, Alex and Manny and Greg (from bringing this up)! Once again, TM to the rescue!