Difficulty Expressing Thoughts

expiiplus1

First off I'm seventeen, so perhaps this problem will go away with age.
1. I often accidentally use the wrong tenses. Ex: "I hear you get a muffin"
2. I often put adverbs in weird places
3. Extremely frequently I substitute a similar sounding word for the one I had in mind. For example I might mean contrapositive and I would say converse.
4. Occasionally I lose where I am in sentences and start using verbal fillers - err emm and the like.
5. I explain things extraordinarily badly - often using much longer words than I should for the given audience.
My IQ is above average, the verbal part being my specialty. I also have few problems in written English - it's speech that is the problem. In addition, despite the stilted writing style of this post I'm not autistic.
People rarely/never notice these problems. I, on the other hand, do and they irrate me immensely. My questions are; are they due to a speech impediment? If so, what can I do to rectify them?

expiiplus1

I should also mention that people comment that I speak extremely fast.
Also my mother says she feels that she often feels that she suffers from a "mental block" where ideas are perfectly clear in her head but phrasing them becomes a challenge. I think this sums up my symptoms too.