Sweet; a composition for Brass! I'd first like to say that I like the ideas that you have going here.
There are, however, some range issues. Nothing you have written is out of playable range, but it would take a very experianced player to jump around so many different registers of the horn within the same measure at that tempo. I'd hate to see the look on the trombone guy's face if you were to hand him this piece; no ideal place for a breath either.
You expect an extensive range on the french horn too, I see. You don't go out of range here either, but you could say that there is no real range limit with a french horn- just a range at which expecting someone to play it with a good sound is impractical. Playing so many running notes that high on a standard double F/Eb horn is also a challenge because your open intervals are so close together (you can essentially play all the notes in high registers like that without fingerings).
The Tuba part gets rather high for a tuba, too. that top line A in Bass clef is equivelent to a B above the staff for a french horn in treble clef. and then later in the piece you go all the way down to a pedel F!
Overall, it would probably be a good idea to rewrite it for a larger ensemble or spreading the parts out a bit better so that the range is not as impractical and sparatic. I wasn't too fond of the repetative trumpet section of the piece, but it's your piece. Anyhow, write more for brass!