When you do the internet connection setup and test, what kind of NAT is detected on your network?
As has been already mentioned, there are essentially 3 ways that you will ideally want to have your network done in a basic configuration. Port forwarding which you apparently tried (curious what ports you forwarded btw). There’s also DMZ which someone else mentioned which enables all traffic for the IP that you set your PS3 to. You can also go with UPNP where your PS3 will request the appropriate ports to be opened on your router as needed. It should also be noted that UPNP is the only setup where you don’t have to setup a static IP on your PS3.
Another option since you mentioned wireless is to change the channel that your wireless is broadcasting on. Since everything pretty much uses the exact same frequency, multiple devices on the same channel can cause interrupts in wireless traffic. If your router supports it, do a site survey and see what channel (1,6, or 11) is the least congested, and change your wireless to use that channel.
Also, if your router uses external antennae and, say, you’re in a two story house, you might want to reposition the antennae so they are giving out the strongest connection possible to your gaming devices.
If that doesn’t fix it, then it’s going to be either something strange like what Sam mentioned with the cable, or you have a more complex setup, and a more complex solution might be what’s needed.