Lukemac, I would look into stealth dyslexia. I just finished reading the dyslexic advantage by the Eides. It has a great section on memory and why someone who is dyslexic is both the family historian and can remember those things better than anyone but has a hard time with procedural learning. The book gives a lot of descriptions of how bright dyslexics are and the entire time I truly just thought of PG kids from early infancy. Most of their descriptions could easily apply to PG kids too.
Dyslexics can read and very often teach themselves by memorizing words but have a hard time with phonics. Some read very well early on but on closer examination have certain problems with reading. It does not always mean trouble with overall reading. My son for example cannot sound out nonsense words and will skip words like to or the when reading out loud. My son improves the grammar in the Magic Tree House series because he reads what it should say rather than what it does say! He is a self taught fluent reader before 5 testing at 7yo at 5th grade level and he is dyslexic.
I would think that your GATES testing where he did poorly on reading and did not qualify for the gifted program might make sense given a dyslexic reading ability (skip words, etc). It is easy to make mistakes on a test if you skip words or do word substitutions.
The Mislabeled Child by the Eides has different chapters on different learning problems including ADD, dyslexia and Autism/Aspergers. I know you mentioned those before. You could read this and see if any of them fit, too.
