I stutter in normal speech as well, but I can definitely recognize what you're talking about. Most of a person's stutter is psychological, there's the old iceberg analogy that only 10% is actually visible to others. When I'm emotionally invested, angry or excited or sad etc and I say something, I barely stutter at all, because the feelings overshadow the otherwise constant thoughts of "oh I've gotta watch out on this word ; I'm probably gonna have trouble here"... Etc. So yeah, when I've been in line for a few minutes and rehearsed "hi I'd like a burger and large fries" over and over again while analyzing it thoroughly, my stutter is much worse than if I was caught off guard and had to answer in the same moment as I thought of it.