Autism

Delayed processing is not exactly uncommon in autistic people. My husband knows not to repeat himself immediately when I ask "what did you say?" because usually I heard him just fine and just need a minute or two to process. Him repeating himself actually stops the processing and I need to start again.

There's a pretty interesting book that also explains this quite well: "Sensory perceptual issues in autism and Asperger's syndrome" by Olga Bogdashina. It's a bit older which explains the title but still very interesting.

I have this when people talk to me. I often say something like "sorry, what?" Even though I heard them Ok, my brain needs time to process it. You might want to look at

https://en.wikipedia.org/wiki/Auditory_processing_disorder

And

https://en.wikipedia.org/wiki/Sensory_processing_disorder

Those articles have the basics

Buffer gets full. Also when reading you may want to slow down. If a paragraph is too much take it one sentence at a time. If that's still too much keep slowing down. It's fine to take your time at things.

Go back and read this one sentence at a time.

I feel you can hardly think and talk at the same time

Or maybe am autistic too? When I'm talking I talk and will need to stop to think

Sometimes I hear/read the words and could tell you what the words were, but my brain lags on processing meaning. I've had to reread so many things because I forgot the part where I actually understand what I just read.