How do I speak as good as I write?

Hmm. Well, there is the possibility of you writing everything onto a machine that will speak it for you. Of course, I don't think that's realy what you had in mind. I think that confidence may be an issue, or, perhaps, the speed at which your brain works to put together the words and tones. Both of these, even if they are not the problem here, are good to work on.