Why do people seem to speak too fast when they talk to me?

People don’t always talk to me. Actually, barely anybody talks to me. But when they do, it takes me a second to comprehend what they say. When the words come out, they are all jumbled up and sometimes I ask them to repeat what they say.
I am much better at reading a letter than I am at listening to a lecture. It helps the information sink in and I can understand it faster. When people speak, it almost goes past my ears before I catch it at all. I am a very advent reader. I read all the time, and it’s easy to picture the conversations. My social time is very limited because, quite frankly, I don’t like conversing with my peers. I am only thirteen years old, but it is hard to keep a conversation at school because nobody understands my thinking process. And, therefore, it becomes very boring very fast.

I am often told that I speak very slow. This is mostly because I choose my words carefully, but it’s also because I need to comprehend what I say before I say it. When I speak, it’s like the words are being spoken by another person outside my body. It takes me a while to understand what I’m going to say.

When I am asked a question like ‘are you goth?’, I just stand there in silence for a few moments then reply (’...’ indicates about a two second pause) ‘no… I just wear black all the time because I stain my clothes a lot… And don’t ask me if I’m E mo (spelling it like this prevents spelling errors) ... because I am NOT one of those wrist-cutters’.

I don’t understand why I speak so slow, it’s like if I speak any faster, my words will get jumbled up and become incoherent. A person once told me it sounds like I think very hard about my words as I’m saying them. I also don’t understand why it takes a while for me to comprehend what people are saying.
If you can answer my questions I will be most thankful.