depending on model number, there may be a width adjustment,
may be accessible internally ...

I bet the 'cropping' you are seeing is the halfbaked way the broadcasters are converting HD signals.

If you have a DVD connected, are the pictures from it normal?

Otherwise the width adjustment may do it. I had a tv make a zap sound, and the picture was suddenly squeezed top and bottom. Adjusted picture size and expected it to fail, but as far as I know, it's still working, 20 years later.