If you do well in writing I would suspect you have a slight issue multitasking. People think talking is one thing, but you get activation both in the part of the brain that processes speech and the part that produces speech. There could also be a damage to the part producing speech even if that is more unlikely. Also I wonder if you are right handed or a true leftie. Many lefties have language in both sides of the brain and have to always connect between hemispheres when using language. For some it can be an advantage, for some a disadvantage.