This is very interesting, coledg.
I don't believe, though, that you're the only person who can write down what you want to say and then say it, but you can't talk otherwise. What you are describing is not terribly unusual in people with severe stuttering (disfluency).
I think there are many others like you. I have known people with severe dysfluency (stuttering) who can sing, or read aloud, but have extreme difficulty with fluid, unplanned discussions - to the point they can't carry on conversations.
I also don't think your stuttering is due to damage to your vocal chords. What you are describing is a brain injury, not injured vocal chords. If you were stuttering due to vocal chord injuries, you wouldn't be able to sing or read what you've written. Your vocal chords sounds completely fine.
Stuttering commonly occurs in adults after a TBI. This is really something a cognitive therapist who specializes in adults with brain injury could help you most with.
Have they actually tested your blood to determine that you did in fact have an exposure to a toxic heavy metal? Which one or ones, do you recall?
You're obviously otherwise functioning at a normal level. You're married, have a baby on the way, can write and think clearly, and are working in a physically demanding job.
At your young age I think there is real hope that you will be able to advance and recover some more of your speech with the right therapist.
Welcome to the MedHelp forum!
Inability to speak spontaneously is also a type of aphasia. The symptoms of aphasia depend on the region of brain involved and the extent of damage. So you may be able to read, write, sing etc but not speak spontaneously. The sad part is that there is no successful treatment for any kind of aphasia. Still discuss with a psychotherapist, speech therapist and neurologist. Take care!