Shaky Picture only during Advertisement or......

Question

I have a problem with my TV as far as a shaky picture whenever there is text on the screen such as a phone number for an advertisement or if I bring up the digital TV guide on the screen or anything along those lines. Even an old black and white TV show will make it shaky as well. I have had digital cable with the converter box for years and thought maybe the box was going bad? Or is it the TV itself? I thought I had found the solution with a bad cable end connection but that ended up not being the problem. My TV is a Mitsubishi SC27403