Re: High Register Tone
try working overtones(playing the P8, P12, P15, M17, etc. while fingering the root. I.E. Finger Low Bb and adjust your embeschure to play Middle Bb, Middle Eb, High Bb, High D, etc.)
Try a few things.
1) Go up the series over a single fingering
2) Play up chromaticaly on one harmonic level
3) Match the sound of the harmonic to the natural fingering
Then just try adjusting your embeschure. Open your throat, take more mouthpeice it, etc.