I have 3 ps's, fios 160/65 actiontec gigabit router, I had this problem once on one ps3, I dont remember how i fixed it, just make sure your network settings are set to manual and select Full Duplex in the internet settings, I leave UPNP off, and I have my firewall disabled completely, I have no problems anymore.
I believe I restored Database, formatted completely, set to default settings now that I think about it.
I worked in IT / Gaming for many years, if you have any other questions feel free to ask.