At the begining of this year i made lead bone in the jazz ensemble at my school. generally, things have gone fine, ive been playing alright, the higher notes are are coming along, i occasionally have to stop to count leger lines to know what im playing but thats okay; theres just one thing that really seems to hold me back. im posting this here, because most of you seem to be sensible people who generally know what youre talking about. My chops are quite terrible. i can only play for so long, and they're gone. i play everday, with all the free time i can spare. im also involved in choir and problably in like every performing ensemble in my highschool. so i put in the time i can. the endurance issue just seems to be really holding me back. I know theres no magic pill or fairy dust, but any suggestions as to remedying the situation would be much obliged. any specific exercises, or lip slurs that have worked for you would be wonderful.

If you're using your 42T to play lead in a big band, that's probably a big part of your problem right there. Unless you're Robin Eubanks (or a very few select others), a big horn is just not the right tool for the job.
Other than that, remember that lead playing isn't something you do over night. It's going to take time.
Make sure you're not putting any more mouthpiece pressure than necessary. Relax. Let a strong, focused, and controlled airstream do it's fair share of the work.
If you have a private teacher, get his or her input. There are a lot of minor things you could be doing that are working against you, but without seeing and hearing you play, I couldn't tell ya.

One more thing (mouthpiece pressure was my first thought) would be:

How is your warmup? A good warmup can lead to great playing all day long, while a not-so-great warmup can lead to early disaster and shot chops.

Your warmup should be specific to both you and the music you are playing at the time, but it needs to be there. Just an example (and this is only me, this will vary person to person) if I am going to sit down and practice/reherse for 2-3 hours, my warmup lasts around 20-25 minutes, and includes lots of long tones, pedals, lip slurs, pedals, articulations, pedals, range exercises, pedals, and more pedals. Then more of all of them.

Remember, that is just mine. You should find one that works for you, especially with limitted time being in school. Here are a couple good books that I shaped my warmup routine around:

"A Singing Approach to Trombone" by Charlie Vernon
"Ben's Basics" by Ben Van Dijk