I have the DirecTV HD DVR, so not positive if this will work for you. On your remote, there should be a button on the top left under TV input labeled Format. Push that until you get a setting that works. I have mine set to pillar box, so that I can see the whole image.
On my DTV receiver the standard definition is stretched bad, the heads are cut off and your can't even see the channel logo in the bottom right hand corner. I have already messed with the T.V. (Samsung LED 8000 Series)settings and had no luck fixing the problem. Is there a way to fix stretch?