How long are your sprints? Im no track star, but you should have a lean out of the blocks (if you start from a sprinter's stance rather than starting on the fly) through the acceleration stage, but your posture becomes more vertical as you maintain the speed over distance. Find some vids of a 400 meeter sprint on youtube. Looks like a very fast run. Hills do help keep the lean. I have a 30 yard dam i run up and can keep the lean to the top, but i have a 180 yard hill i sprint up that starts out gradual, increases to a very steep grade for about 60 yards, and levels out a bit after that. The lean is almost gone when i reach the top.
Also, if you start from a sprinters stance, or from a dead stop in any stance, be careful. i popped a calf after about 6 months of regular hill sprints. Warmed up good and everything. Blasting out of the blocks up hill is very stressful on the calves. I saw a vid of Riptoe giving Wendler shit about the same thing, following Wendler's advice and tearing a calf. Also, my wife tore a calf a few months earlier doing hills with me. I thought she was just in bad shape, then ate crow when it happened to me. I think it is safer for regular guys to start the sprint on the fly. That's what i do now and so far, no more problems.