Auto channel can cause signal lost because the router has been trying to avoid the other router channels. There are "three" main channels, 1, 6, and 11. The other channels are the side band channels of these three channel. Usually use manual selection channels 1, 6, or 11 should prevent signal drop. Most people use channel 11. Most home phone devices use channel 6. Therefore, you should use channel 1. Just place the computers at the line of sight direction of the front router so that the router signal cannot be cancelled out by the nearby routers, and the computers can receive the max strength signals from the router.
The poor wireless down could be the FIREWALL setting (use endpoint independent), enable QoS settings, and enable UPnP and Multicast Streams. I set the uplink speed at 55,000 instead of auto detect, Beacon with 33, RTS/Frag threshold at 5,000 to boost up the performance of the router.
I have tried on my dir-655 A4 router with firmwares 1.21NA, 1.32NA, 1.33NA, 1.34NA, 1.35NA, 1.21EU, 1.31EU, 1.34EU, 1.31RU, and 1.34WW. Firmwares 1.33NA, 1.31EU, 1.34EU, 1.31RU, and 1.34WW are the most stable upload/download firmwares. Personally I ended up with 1.31RU (English) firmware for its speed and stable performance.