Check out these articles...
http://www.tomshardware.com/picturestory/571-wi-fi-beamforming-networking.html
http://www.tomshardware.com/reviews/wi-fi-performance,2985.html
They will help a lot.
13 dBm may be a result of interference with other wireless devices. I could be possible to change channels to help avoid this.(it's in the article --> channels==frequencies) The farther distance in frequency the less interferance will be resulting. Think of it like radio stations 99.1 and 99.2 are very hard to separate and give good listening music. But 99.1 and 105.9 have no issues and sound great.
Your antenna gain should not be set that high. Think about the TX power as the distance projection and the dBi as the shape of the radio waves being projected from the antenna.
The higher the TX power the further distance that you can be way or the more **bleep** can be between the laptop and the router. But be careful the higher this setting gets the more likely you will burnout the radio. Yes it's possible. I think the max is around 251 dBm
Image a shape that is perpendicular to the antenna(s).
1 dBi representation is a sphere O
5 dBi is more like a classic UFO shape <>
10 dBi is like a disk --
15 dBi is like a thin disk --
@ 192 dBi your making it a laser beam (good for 100ft but bad for 20ft)
Granted that the shape changes as soon as it comes in contact with a object. Sound moves well through air but not through walls or metals. The more tweaking you do the better it will get. However, the more you push it the closer you are to damaging the radios.
Not Supported under Warranty!!! (I think)
The other thing to try is set to TKIP and go to your laptop and force it to use TKIP. If it no longer connects, reboot and try again (sometimes it hangs). If it still doesn't work switch them to AES and try again.
Weird why isn't any buffalo Tech's chimming in right now???? Hello.........???