I had a 30+ year career in IT even with a stammer. IT is an excellent place to be with a stammer because people are focused more on the work being done than on the personality behind it. And lets face it, IT is filled with interestingly different people. I'd wager you are judging yourself far more harshly than others. Stop doing that. It's all about confidence and familiarity. As you feel more comfortable in the role and around the people you work with, your confidence will grow. That confidence will translate into not caring if you stammer or not: you are you and you speak the way you speak. They hired you so they weren't judging you on your stammer then, like they aren't judging you on your stammer now. It's all about getting the work done and being a good colleague.