Why do I have trouble slurring the higher I go? And it's not even that high. What are ways to improve it in practice? And I recently switched mouth pieces, but I tried to switch back to the old one but it hurts and leaves a mark above my mouth so I'm sticking with the new one. It doesn't hurt at all. And the old one has always left a mark above my mouth, even when I tried my best to use little pressure so I'm sticking with the new one no matter what. How long will it take for me to completely adjust to it and build my range back up?