This, of course, is why one needs to practice.
I have written and read aloud academic papers. Lee Gold noted that the sound of an academic paper is not as critical as the sound of a poem, but I disagree. In 2007, I presented a very well received paper at MythCon. ellen_kushner complimented me, saying that, in the entire paper, there was only one sentence that was not harmonious. This is why I rehearsed and rehearsed.
I also rehearse to get my reading speed down. Before I gave my very first paper, at the ICFA, cattitude gave me much valuable advice, including what to do when running short on time. "The one thing you are not permitted to do," he said, "is to speed up."
As anyone who has met me can attest, my natural speaking speed is rapid. I practice reading my papers as slowly as I can bear. This gets my reading speed down to "Yes, you were a little fast, but we could understand everything."
I rehearse to see what phrases I will trip over. One of my teachers in grad school, Professor Catherine McKenna, once talked about a paper she delivered on some of the tales in the Mabinogion. If I remember correctly: She explained that, in Welsh, the possessive is "of PROPER NOUN", rather than "PROPER NOUN-suffix". She read aloud a paper with such words as "Pwyll's" and "Rhiannon's", and quickly discovered that these words are veritable tongue twisters.
I read aloud to see what sentences work. A paper that is read by a reader can have convoluted syntax. The reader can, if need be, look back and reread a sentence or a paragraph. But, if you're listening to the paper, a tangled sentence breaks your concentration. By the time you've figured out what I've said, or failed to figure it out, you've missed the next sentence. So, I want to make sure that my syntax is blazingly obvious. This may not mean short sentences, but it must mean clear ones.
And, there's questions of emphasis, especially when I quote.
When Neil Gaiman read chapter one of The Graveyard Book aloud at Columbia, he was asked if the publisher made him read all of his books aloud, for audio books. He replied that the publisher did not "make" him do this. The publisher allowed him to do this. Not all authors are good at reading aloud, he said, and, indeed, most are not.
As anyone who has ever heard him can attest, Neil Gaiman reads aloud very, very well. Anyone who has not ever heard him read aloud is encouraged to do so. He reads the entire novel The Graveyard Book. Listen. Watch him. Then, watch and listen again. Look at what he does and how he does it.
Another author who reads aloud very well is Catherynne Valente. She reads aloud sections from The Orphan's Tales. No video, but listen.