Xbox360 output and Vizio TVs

I just bought a 1080p Vizio and when I play an Xbox 360 game, just out of curiosity I hit the Info button on the Vizio remote. It showed the output as 720p, which confused me a little since I thought the 360 could output 1080p. Did anyone else have that happen, or does the 360 slim only do 720p? Thanks

No, I didn't even know that was an option. I set it to 1080p in the video settings and that fixed it. Now there seems to be an echo for voices when I play games or watch movie previews. Any idea how to fix that?

I changed the Discovery setting or something like that on the console, and that fixed it. Thanks for the help