Thanks for the reply, mco; here are some of my "answers:"
1. Updated adapter driver
Done. Now running the 1.33NA firmware. Funny story there, too. When I just hit the "Update Firmware" button, it told me my old firmware was the most recent; so, I had to that update manually.
2. WPA2/AES encryption
Done. This is actually all I ever used.
3. Auto channel width (20/20) on router and adapter
Did you mean 20/40 auto? 20/20 isn't an option. If the first is what you meant, then done.
4. Enable WMM on router and adapter
Done on the router. Since I'm running Linux, I'm not even quite sure how to enable this on the adapter; looking into it.
5. Ensure QoS enabled on router
Done.
1. Turn off GI something on router
Trying this now. Any idea what "Short GI" really does, any way?
2. Tweak various adapter settings (highest roaming aggressiveness, ad-hoc power mgmt set to "noisy environment", something with throughout enhancement, etc) - essentially trial and error; change one thing at a time and see what happens. Sure your adapter has different things you can tweak than mine
Like I wrote above, I'll have to play around and figure-out how to tweak these things in Linux; I'm sure there's no easy way.
Thanks for the well-wishes and all the help!