If your Airport Extreme is dual band (2.4 and 5 GHz) capable, be sure the 5GHz band is enabled. It might make a difference.
I would except the Airport Utility installed with my 10.8.5 Mountain Lion will not configure an older Airport Extreme. Apple won't allow me even to see the settings - it just has the spinning bars ad infinitum.
Boo, hiss, Apple.
It sure looks like an attempt to force a user into spending a pile of dough on a newer Extreme. I know the new standard is much faster but, to be honest, I'm in no hurry and the old standard is just fine.
