You should try > Menu > Parental, Fav's & Setup > System Setup > HDTV > Video > Native On > TV Ratio > Widescreen 16:9 > TV RES > 480p, 720p, and 1080i selected.
Just suggestions. Each setup is different. Native on is going to make the channels change slower, but this is what gives me the best picture. Best of luck.
Also, you might need to look into whether or not your tv is stretching or zooming the picture.
While we're in here you might want to pop over to the display menu and turn the scrolling effects off for the on screen menus. This makes the guide a little less slow.
