Is it fingers, or support, or embouchure? I should think different things could help different problems, that's all!
One thing that I have found helps in the 3rd octave, is when playing scales that I know well, I have been adding a note at a time to the top, and still playing at the same speed. So for example when I practice C major now I am playing up to G3 at crotchet = 130. I have found this helps with everything really. I should think longtones in the 3rd octave should help with embouchure and support?
For scales and just getting your fingers moving faster, try
splurts if you haven't already. I find they really help getting things going faster.
This was one of the threads that had a lot of scale stuff in it. Should have a rummage and link some more scale things shouldn't I?

Masses of tone and scale threads in Viva WW, I periodically have a check back as there are some reeeeally useful threads languishing in the back pages!
Hope any of this helps...

ps I find the top octave depressingly hard to improve, I think it's hard for everyone *wry grin* (unless someone comes along and proves me wrong...) you are not alone!
pps... just a thought, have you any 3rd octave workbooks?
Ones I know of: the Filas high-register studies (two different books)
Simon Hunt - Scaling the Heights.