Hill sprints are "different". I'm guessing you're sprinting up, jogging down?
They work you different than a level sprint. You have to reach out and up with your lead foot, and get more "up" as you push off. For me, it was shorten my stride, speed it up, and use my arms more. Also, you don't want to slow as you top out on the hill.
Personally, I would find the meanest hill with sandy or muddy soil. Blast up and over the top, then gentle jog it back down.
Also practice your downs - some people lean back and take it slow. If the course is wide enough, you may be able to pass them.
Since you're running CC, maybe take another guy from the team. Give him a head start, see if you can catch and pass him. Do this for short sprints and take turns.