Two things have to happen to play in the high register- 1. The embouchure must have your lips in a position to vibrate fast and free. 2. The fuel to the embouchure (air) must be energized (air velocity) to get the lips vibrating. Think of the lips as energy resisters. So the chops can vibrate, develop the embouchure muscles through isometric training. This allows you to use less pressure, the lips vibrate better, more freely. Make sure you have the highest lip efficiency. Mouthpiece placement over the pressure point, and be sure to place outside the red of the lip (inner and outer rim!). Pressure on the firmer stuff outside the red. To produce much faster vibrations you increase air velocity (not volume) and power. Do breathing exercises (that you Bobby Shew). Through the sound, make sure tongue position is correct. Do Flexibility exercises, pivot exercises, allow the tongue to find it's position for the upper register. The sound tells you when it's right. The aperture must become smaller for the high register. Flex and range studies making sure not to blast out the high notes so your aperture will learn how to get smaller. Forcing the high register frezzes the lip motionless, it can't change size. Do isometric exercises for more embouchure strength and aperture control. Make sure you are not in a more puckered position, or a more pinched position. Both "MM" in the lips and "OO" at the corners are needed to control aperture size and keep it's shape. The Double High range needs coordination, finese, skill. Not strength! This is an area for "Strength is my enemy, weekness is my friend." If you try playing in this range with more force you will fight the pipe. To play up there you are using more finese and control, and once you get it down you can usually do it all night becuase it's not such physical effort. Try it.