if you live by yourself, or if you family or roommates dont mind, what you can do is try by passing your router altogether and connect your ps3 directly to your cable/dsl modem.
basically this removes the router from the equation, so if you are still having problems, it may be related to your ISP. one possibility is a bad ethernet cable, so consider buying a brand new one just in case. without the router in between, there should be no firewall issues. however, since your router wouldnt be connected, that obviously means no one else in your household can get online. at least then, you wont expose your PC to the internet without a firewall.
an alternative would be to disable the firewall on your router, and download/install a personal firewall on your PC. i would not recommend that tho, as most personal firewalls are kinda garbage (or at least the free ones are. you would have to pay for a decent/brand name one).
just something to try. if you find that you do not have issues at all, when you are connected directly, that could mean the problems you get while connected through your router may be related to the router. either the router is faulty, or the configuration is faulty. one way to avoid completely disabling your router is putting the IP/MAC Address of your PS3 in the DMZ of your router. this is supposed to effectively act like your PS3 is outside of the firewall (it should act as if it directly connected to your internet, instead of through your router). however, i have seen people claim they still have problems even after putting their PS3 in the DMZ. *shrugs*
hope this helps.