The key to memorizing a speech is to memorize it hierarchically. You begin with the broad chunks, moving to specific paragraphs, phrases, up until the intonation and your timing with the words.
When starting with the chunks you simply write out the main points of the speech then cover them up and recall them.
Moving up to the small points you can expand your bullets to represent each idea with one or two key words and quiz yourself until you have it memorized.