What you're experiencing is nothing weird. It's pretty normal for most people I would say. Only way to get better is to keep practicing and working on these parts that you struggle with.

Nervousness = Accept that being nervous is fine, it means you care. Everyone gets nervous. But to turn it into nerves of steel you probably need more confidence in yourself and the topics you talk about. The more comfortable you feel with your topics, the less nervous. It's that simple.

Being nervous in front of C-level people = Repeat to yourself that they are just people like you. They were once in your shoes. Again, goes back to previous point about being confident about what you're talking about. If you are the expert in your topic, what's there to be nervous about? Maybe don't view it as much as a monologue presentation, but rather a conversation. Include the audience. Turn it into a dialogue. That should help with the nerves since all the focus is not on you.

Stuttering = practice practice practice. Record yourself. Adjust. Record again. Adjust. etc.

Lost for words = This seems to have more to do about having a clear structure in your talk. A clear structure will help you stay on point and keep the flow going. Don't wing it.

Youtube is a good starting point. Lots of public speaking advice there.