Spent 8 years in the Army. 4 years of it was active duty infantry. You'll be fine. They'll focus on you more at first (especially in boot camp / basic), which means you need to know your shit and be good at it. Military primarily focuses on if you're able to complete the task and how well you complete it. So do everything you can to be a stud. There's probably no tips on stuttering anyone can give you here that you haven't heard a hundred times. Just build that confidence up, and know your shit.