If that doesn't fix the issue the issue might be with the settings in the box producing the signal (cable box, DVD, etc). It also could just be a bad broadcast. Several cable channels are known for their butchering of aspect ratios to "fill" the screen.
Wide Mode is set to "Full" but the picture is still zoomed. The tops of headed are chopped off & text in commercials runs off the edges. Same story on HD channels & non.
How do I fix this?
In the Screen settings:
Wide Mode: Full
Auto Wide: On
(gray & unchangeable) 4:3 Default: Wide Zoom
Display Area: Normal
(gray & unchangeable) Horizontal Center: 0
(gray & unchangeable) Vertical Center: 0