I have this problem. Here's something I wrote about it, in case that's any help. I get violently angry when overloaded, but when I'm en route to be overloaded, I have verbal communication issues similar to what you describe.

I'd suggest looking into Sensory Processing Disorder for self-help topics, but unfortunately, that may not be a useful angle for professional help. The condition is not recognized in the DSM or ICD, it's considered "controversial" diagnosis, and when it is used, it's diagnosed based on manuals like "Diagnostic Classification of Mental Health and Developmental Disorders in Infancy and Early Childhood." Most of what I've heard about the treatments for it sound incredibly useless for grown-ups anyway. My doctor couldn't figure out what I was talking about.

The Highly Sensitive Person concept might also be a useful resource.

I haven't tried it out yet, but I considered making a 1-to-10 for communicating my current state of overload to friends and family. (You have to tell them about the scale in advance, when you're feeling good, then you'd just say a number later when you're feeling icantwords.) Not sure how well that would go over in a work environment.

It's hard to tell, but I think my ADHD meds (mixed amphetamine salts aka Adderall) help somewhat. If so, it's a fairly small difference.