#1
I've recently began playing guitar up in the Senior Jazz Band at my highschool, and I've been given a solo (i think our director picked the chart mostly for me to learn leads, as I also play all the lead horn lines) but find I don't build up to a climax and run out of steam halfway through

http://www.sjsd.net/~gedwards/S027ED123.10/Old%20School.mp3

could I have some advice for building up and working with the backgrounds?
#2
Listen to where the dynamics in piece are and try to mirror them. Use bursts of speed tastefully to build tension. Listen to other people's solos and try to figure out where they put their tense moments and how they resolve them. Assuming you're playing on guitar, try to figure out a solo on horn and transpose it to guitar. Different instruments breed different ideas; that's why a lot of jazz guitarists transpose piano, horn, and sax lines and classical guitarists do the same for piano and violin.

Another idea I like to use in my playing is build up to the final point of resolution with accidental runs and diminished/augmented arpeggios. It works really well, especially if you use the major seventh of the resolution point as the tonal center of those runs.