Intonation

How can you maintain sharpness when speaking reasonably fast?
By sharpness I mean like when I say 'order', I sort of mumble or murmur 'der' part unintentionally, i.e it's not sharp all the way to the end.
So some people can only hear 'or' part and ask me again. If I say it slowly or word by word, I am almost like native speaker but when those word get into sentence, it's chaos for both me and the listeners.