Where are you seeing this NAT3 at? This on the PS3 or the router? Are you on DSL or Cable ISP? How are you connecting the PS3? Wired or Wireless?
Where did you get the v1.21 update from? I presume from the main web page. I would recommend getting the Beta as the released v1.21NA has proven to be problematic. Current v1.22 Beta 03 is working well.
I don't have a PS3 and my post here is tuned for Xbox in the Gaming and GameFuel section:
http://forums.dlink.com/index.php?topic=10435.0However, all other options could work for you if you give them a try. Making adjustments for PS3 in Gaming and GameFuel.
I hope maybe someone else that has a PS3 will help you out as well. Please send me a PM with your PS3 gaming and Gamefuel settings, if you can get it working well. I'd like to add them to the Gaming and Gamefuel post for other users to review. Let us know.
I would presume that when and if you get the FW updated, run the router with out changing anything, if you don't see a change on the PS3, use my Gaming and GameFuel instructions and try. If that doesn't seem to effect any change still, I might call DLink and or PS3 people and ask them if there is any known issues with this router and the PS3. Sometimes the PS3 people have some info about different routers and cant give you specific setup options to use.
Remember, perform the following steps is recommended:
1. Save the 4500's current Configuration file. You can reload this later. Save time on reconfiguration.
2. Update the FW.
3. Perform a Factory Reset after the FW update.
4. Check PS3 functionality. Ensure the PS3 is set to automatically obtain IP addressing.
5. Load configuration file if needed or tweak the router as needed.
Keep us posted.