In both the cases you mention, pronunciation can seem a little off simply because the reader is moving a little too fast, and syllables and/or sounds begin to run together. Experienced English speakers can be prone to this. If you happen not to be an experienced speaker, I recommend you mention this effect to whomever you are speaking to, whenever it happens. If it's a teacher, make sure the teacher knows that your goal is better familiarity with the language.
If you are an experienced speaker and do not have this happening to you, then I salute you. But there is the opposite problem to watch out for: that your speech may be slow and seem to drag on for your listeners. That can happen: we try so hard to avoid one problem and in doing so run directly into the opposite.