Hello, I am having a similar problem with my DIR-657 wireless connection.
It's A1, 1.01, 11bgn, 20/40, channel 6 (AUTO), TKIP and AES, cable modem.
I don't use the wireless connection, but my family members are having trouble connecting/staying connected.
If I reboot the router I can connect, but eventually devices are dropped, and won't reconnect without another reboot.
I will have to test how long connections are lasting, but I've been able to connect phones, ipad, kindle, wii, tv, and have had the same problem with all devices.
I will try some of the suggestions in this thread, but it will take some time as I am just learning.