Best advice I can give: slow down.

Especially if you're nervous, a short time on stage can feel like an eternity so your immediate impulse is to talk quickly and fill every pause with speech. That's what's wrong with "uhhs," you tend to say "uhh" more than you normally would in conversation.

I had a professor who was a fantastic presenter and would pause frequently and for about 5-10 seconds to allow what he just said to "sink in." Then he'd smile and continue. Don't be afraid to do that. It's natural to pause and think about what you are going to say, even if you are giving a prepared speech.