Only thing I could recommend might be to factory reset, reload FW, factory reset once again and set up from scratch.
Ya, I'm going to recommend that you step up to a DIR-655 or better router with better QoS engine since you are gamers. The 651 might be good for a single gamer or mom an pop kind of traffic. There are some basic routers out there that are ok however not as good for gaming. I have the 655, all 3 Revs and each one is good for gaming and are stable.
You need QoS engne with customizable settings like this:
Gaming and QoS for XBLIf you want to so some future proofing, then maybe a DIR 8 series dual band router might be something to look at. I have a few and all are good with gaming too.
What are your network and WiFi needs? What do your current devices support as far as WiFi? N or any new AC modes? Let us know so we can help you find a good router for gaming and such.