Thanks, that could be it. Maybe he just isn't interested in the worksheets, etc. My oldest dd was the same way now that I think about it and she tests near PG.
It's tough not to doubt the giftedness though. I have a friend who really pushes her kids to sit and do academic type worksheets everyday. I think they are all close to MG but all read by the time they are 4 - 4 1/2. I've just started to doubt my kids ability or even my competence as a parent when I'm not moving them ahead well before hitting K.