1. If you check your internet connection from the PS3 while wired to the DIR-655, does it show UPnP enabled and Nat Type 2?
2. Are you noticing any other suspecious behavior from the router, such as login timeouts or slow page loading from other machines?
I have my PS3 wired and I've had lag trouble with the router which has required me to reboot it and then things are ok. But I haven't had trouble with being booted out, since I changed my MTU on my router to 1492, as was required by my PPPoE DSL connection.
Also, are you doing double NAT? Meaning, is your modem performing NAT as well as the DIR 655? If so, consider putting the modem into bridge mode which will allow the router to talk with the ISP over PPPoE or PPPoA I belive... Doing NAT on the modem as well as the router might slow things down a little more. If you're not sure how to do this... You'll need to write down the connection settings to your ISP, such as your ISP login username and password, as well as DNS settings that your modem is using. Do this first before changing things.