Good luck on gaming with that connection. UpNp is only needed if you want to create a media server on your computer so that it can stream music, videos, and pictures to your ps3. The most important thing is the fact that you have a NAT 1 connection.
If you are really concerned with security, I would buy a good router, put the Motorola 3347 into bridgemode and then allow the new router to handle security and firewall concerns. That way you can open up the neccessary ports and not have to worry about any possible security attacks.
I have a couple of 3347's around and from time to time try one to replace my 2210...which hasn't failed since the bad ones were culled out years ago. I am not a gamer but use VOIP as my only phone service along with having my ATA behind my router with NAT. I tried every type of connection with the 3347 in bridged mode but never improved what I have now...6 meg down service that actually nets about 5.80. I have the router send VOIP to the ATA with a fixed IP while forwarding the ports. In the past, the only reliable way to guarantee VOIP was to disable the SPI and SIP ALG. I was never convinced that the so-called router firewall did anything. The routers function really only routes correctly to each computer. That's why I always have a software firewall also engaged. Does anyone have a similar setup and have they found a way to improve what I am getting? ATT DSL Southeast..