I really enjoyed this piece so far. I've only listened to the first movement but I've got a few comments. Firstly I liked how you transitioned between one idea to the next and I thought the whole movement flowed very nicely.
Taking a look at the string parts starting at mm 149, you might want to mark divisi and/or think about revoicing some of the chords. Most of them are not playable as quad stops and you're going to end up with an awkward texture since the sections will have to be in 3- or 4-part divisi some of the time. Even if you split the chords into 2-part divisi (which should be beamed accordingly), some of the double stops are very difficult to play at that tempo and may sound pretty dry and pitchy. That might be the sound you're going for though, I'm not sure. =) Whatever the case, just be sure to indicate your intentions in the score so that it's clear what you want the players to do there (and again at mm 232). Also make sure that your string bass doesn't go below written E below the staff at mm 327 or you'll have to indicate a different tuning, which is not recommended.
Is this piece supposed to call for 4 trombones? I was following the 3rd bone part intently to see if it ever goes below C3, and it finally does at mm 163, but at that point there are 4 trombones playing? I was a little confused by that.
Anyway, I'm excited to listen to the rest of your symphony when I get home tonight. Great job!