Its kind of moot at this point, but doesn't the 624 have a SuperG mode, which can double the speed of the G band? This feature only works with cards also capable of it, and sometimes causes problems with cards that don't support the feature. To correct this problem, you have to turn off the SuperG.
I know its of no use now that you have a different router, but that feature can sometimes cause those symptoms and this may be helpful to someone in the future.