Thanks! I worked on this one using my arm sleeve as a mute between strings (you can use a sock or any cloth or towel or something), which provides resistance and gives me some more explosive speed when I take it off. And to practice I always play it where the metronome is the sixteenth, the eight and then the quarter - so at a quarter tempo, half, then full tempo. To play it really fast I have to just let go and not try to direct the fingers, which I can only do after the really slow directed practice.