Stuttering & spontaneity

Stuttering & spontaneity Do you guys stutter more with or without preparation? I have noticed that I am actually pretty good at, say, reading out loud or giving some sort of a virtual presentation (where I can simply read the slides aloud). However, whenever I'm caught off guard or I'm asked something that I didn't prepare for - I stutter/block a lot! This is especially noticeable during competency-based job interviews (the bane of my life) because I basically have to think hard on the spot to come up with a story if it's a question I hadn't already anticipated. I do try to prepare though - If I have already come up with a good story beforehand then it's not so bad but when caught off guard... nightmare.