How do I control pitch other than adjusting mouth piece in or out.

I find that when I play the upper octave my instrument is sharp and on the lower octave I am flat. I have not been playing that long, but I have good tone (smooth, no squeaking etc). I am using a 2 1/2 reed and a Yamaha 4C mouthpiece. It doesn't sound bad when I am playing on my own, but I do play with a group and the sharpness of the upper octave is particularly annoying. I have a tuner and I've adjusted the mouthpiece as much as I can and I cannot get away from being sharp higher and flat lower. The 2 1/2 reed is great...I am not strong enough yet to use a 3 (I've tried). Any suggestions! I can play the horn at length, not tiring ... but there has to be something more I can do without going to a more difficult reed.