I may not really be qualified to give advice, as I don't have the most sparring experience, but I think I have a good analogy for you.
A lot of adults don't learn foreign languages very well. The simple reason being that they over-think it. You want to get everything right; the choice of words, the tense and conjugations, the particles, the pronunciation. You think of what you want to say in your native language, and then try to find the correct way to accurately express it without error in your second language. Usually, this just results in you being lost for words.
But what about your native language? You don't think about what you're going to say very much, usually. You just say it. It comes out instantaneously the moment you need it because you are accustomed to it. You don't even think about it. You don't worry about what to say or how to say it - you just trust that it will come out properly when you open your mouth.
I think that learning a martial art is a lot like learning a language. You have to become accustomed to it to the point that it's second nature. When you're training - or, studying, that is the time to slow down and take the time to check your grammar and pronunciation, and practice those things. But you practice them with the intent of becoming intimately accustomed to them. When you learn a grammar form, for example, don't just use it a few times in a text-book exercise and expect to be able to use it on the fly. Try using it in as many ways as you can; in as many contexts, and with as many words as you can. Do that until it becomes second nature. That way, when you need it outside of practice, you won't stop to think about it -- it'll just be there.