menus on the TV as well as the menus on your other components, that leaves one thing: your DVR's settings. Go into whatever setting are there and make sure its set to output correctly.
Keep in mind, even if your DVR output is set up properly you will still sometimes experience weirdness with broadcast info (cropping, stretching, aspect ratio changes during commercials, HD to SD quality drops during news update screen-crawls broadcast by local channels, etc). Usuallly this is due to bad decisions on the part of the channels themselves... the worst being when they stretch SD content (or crop the tops and bottoms) to "fill" a 16:9 screen.
I have a 42 inch Samsung Plasma with a Comcast DVR HDMI receiver plugged into it.
For the second time in a year with different receivers, I am having issues with the centering of the picture.
On the non-HD channels, the picture will elongate and fit my television screen. On the HD channels, it will do the same thing, but also sometimes go off-center or go off the screen (e.g. with scrolling information on ESPN or CNN the scrolling information will be truncated because it does not fit on the screen). In addition the picture quality is not the same.
I think this is a Comcast issue. I have played around with the Samsung screen view and all Bluray/Roku inputs appear as normal. In addition, I had this exact problem with another receiver six months ago. I traded in the receiver for another one (Scientific Atlanta for a Motorola) and the problem was resolved with the new receiver, but that has only lasted five months before reverting back to the same issue.
I am not sure if others have experiences similar issues. There should be a better solution than swapping out Comcast receivers every six months.