| | There's nothing wrong with your brain.
Your plight is common. There's nothing wrong with your brain. All you need is some training in articulation--and a dash of self-confidence.
Try building up your speaking skills...slowly. Try interacting with a computer audio program--answer the computer's questions, and see how you do.
If you don't have this problem when answering the computer questions...then you know it's confined to interactions with people.
And if that's so, then you're hardly unique. The standard strategies apply.