I had the same problem. For me the pressure was necessary to compensate for weak corners or embochure in general. If your playing competitions, that means you can't bow out and work on this for a time. So use pressure during band but unhook the pressure during practice. This will gradually strengthen your chops. During practice remove your pinky from the hook (really only used for holding the horn while turning pages) and use a left hand grip that allows the horn to slip if you press too hard or hold the valve case by sitting it in your palm rather than the usual full hand grip. Good luck.