Change Nat Type For Internet Service.?

Son’s PS3/Internet game freezes after about 20 minutes of play on MAG. Worked fine until a couple of weeks ago.
Son called Sony. Sony said to change security from WPA2 to WEP open. Did that. Still freezes.
Sony says NAT type in our router configuration needs to be set to 2, instead of 3 (it’s displayed as 3 in the PS3). Can’t change it in PS3. Sony said to call ISP. ISP (AT&T) doesn’t know what I’m talking about. In router configurations, I changed NAT from Secure to Open (no numbers were available to be changed). Still have problem. AT&T changed router settings to channel 11 instead of auto channel for better gaming performance. Still having problem (game freezes after about 20 minutes). Honestly, I think it’s a PS3 problem, but I can’t press that issue until I can change the NAT type to 2 to say we tried. Do you know how to change NAT type?
Equipment: NetGear router Wireless-N 300; Motorola DSL modem 2210-02-1022; PS3 connected through wireless connection via the NetGear router; main computer is a Windows XP Media Center with internet access through ethernet connection via the NetGear router. Connections to the router: ethernet – 1 desktop Windows PC; wireless – 1 laptop, 1 PS3, 1 Wii (not all accessing router at the same time).