There could be many reasons why this is happening to an intelligent individual. Like many have stated, they may be still formulating what they want to say and how they want to say it while using the filler words. I too will say something and realize that it doesn't sound like what I meant so I will reword it.

Like lizardlady, I also have fibromyalgia and I get stuck on words so badly and it's soooooo maddening. I don't consider myself a dumb person, but I too will use filler words (sometimes swear words when I'm frustrated at not getting the word I want LOL) and I can imagine it can be frustrating to the folks I'm talking to.