Dyslexia is really, really, common - conservative estimates put it at 10% of the population. There are many of us on the board with verbally gifted, dyslexic children, and "struggling with letter sounds" is, as aeh notes, a big flag worth investigating.
Dyslexia can look quite different in a gifted child than in typical descriptions, however. When I researched it, I found little that seemed to relate to my child. There are several threads describing experiences of people in the forum which might be helpful, such as this one:
http://giftedissues.davidsongifted.org/BB/ubbthreads.php/topics/217061/Stealth_dyslexia.htmlAuditory processing issues can also lead to children struggling with letter sounds. Note that a regular audiologist/ hearing exam checks physical hearing, but not auditory processing. The latter is more about how the brain interprets the signals it hears, rather than whether it can hear them in the first place. (Here's a basic description:
http://www.caddac.ca/cms/page.php?166)
