Off the top: Maybe try different consonants to get the right tonguing motion for you (eg "D" not "T")? Or maybe try a slightly harder reed? And, oh yeah, start slow and build up speed over a period of several decades ( ). Seriously - use a metronome and don't proceed to faster tonguing until it's absolutely clean and clear at slower speeds. Consult with your teacher over what "clean and clear" is. All the best.