All I can say is train your ear. This was recently posted somewhere: http://www.trumpetguild.org/pdf/2002...0206clinic.pdf
Anyway, I just got back from orchestra, and man I was dead at the end. We pulled out the James Bond Medley, and I covered the first part (I was sight reading since the 1st guy didn't show up today). Since it's a community orchestra we all share the different parts rather than audition for seats. Anyway, I knew I wasn't going to be able to play it, but lo and behold. As soon as I played the first note it was like I was totally fresh and a different player. My sound was awesome and the range was easy. The mental sound model of how James Bond should be played and how it should sound was so strong in me that the horn virtually played itself even though I could barely hack out the end of the previous song. Having a strong internal sound concept and knowing how each particular song should sound is the key to endurance and range (if everything else is working). I'm seriously sold on this idea now.
Another success story is back in high school we did Crazy For You, which is a tough trumpet book. At first, it was so hard, but by the end I was playing it 10 times a week with ease. The shows were almost effortless because the music was so well ingrained in me. This ability did not transfer over to stuff that I didn't know so well. Anyway, I'm probably way behind on this and most people here probably already do singing exercises.