Who are you?
You are interesting, funny, contemplative, intriguing, curious, engaging and more. Why is it when getting up to speak, you leave all of that behind? The audience gets to hear from only a slice of you. The boring informative slice, at best. Then, as soon as you're finished, your whole personality comes back.
What happened?
Thinking back, the role models we had for information were nightly news anchors who were paid to not have personalities. They were (and are) meant to be solely informative. Having an opinion would sway the viewer and that wasn't the purpose of nightly news. Reread that 'having an opinion would sway the viewer'. You WANT to sway your viewer (audience), you want them to know, and be swayed by how you feel about what you're saying. Those opinions and feelings come out in your personality, so please, please, bring all of you to your presentation. Otherwise, it could be...a news anchor.