PS3 lowing resolution in game!!

So I had my ps3 from launch in 06 and I finally decided to by a HDTV. I have a 1080p 37" vizio. I have have my ps3 hooked up to it with an hdmi cable and in the XMB menu the resolution is 1080p. But when ever i go ingame my res drops down to 720p. In not sure why its doing this because im playing pretty new games that say they support 1080p on the box. If anyone has a clue why the resolutions drops whenever I go in game let me know.

Thanks