For a looong time, I had such an aggravating time. Sometimes I could put the horn to my face, and create BEAUTIFUL upper octave notes. Other times, I could hardly play any lick out of Clarke's book without cacking every note, and absolutely missing the register past tune C. Its just figuring out that it isn't so ****ed hard as you think.
Though getting the embochure/aperture/wind collumn to effortlessly switch from low register to upper is difficult to grasp at times.
So is breaking the habit of using hard, diffused wind for the higher range...
Van