I suggest you email your desired college(s) and ask how prominent a role presentations take in your degree. You could also add your concern - mention you have a stutter, and enquire if being exempt from the presentations is an option. Or perhaps you could arrange to give your presentation(s) to just your professor instead of the whole class. Personally, I've had one presentation a year. And I could have gotten out of it if I'd asked - in fact I actually requested to do them anyway.