Thanks to Darren LaCroix and the Champions Edge program, I learned about a documentary of Jerry Seinfeld perfecting an entirely new act after his TV show ended. It's called Comedian.
I swear I will never feel bad about stumbling and mumbling again when I am developing a new speech... and you shouldn't either.
Even Jerry Seinfeld used notes, forgot what he was talking about, said um and ah and er all the time when he was developing his new routine.
He got better... way better and was eventually wowing audiences again after working, and working, and working on his new routine in front of live audiences, refining every word and every bit until... he was Seinfeld again.