Took your suggestion and tried the DTV box on another TV but could not replicate the problem. I was using YWR video connection though (don't have another HD TV). So I tried the YWR video connection on my Panasonic GT30, and the problem was gone. Then I switched to new HDMI cable, and the problem is still gone. So I'm happy as can be. I suspect maybe it was a bad HDMI cable, however, I can't exactly duplicate the problem with the old cable now, though the picture is definitely not as good with the old cable.
Thanks again. Case closed for now.