I bought my tv 3 years ago in a super going out of business sale. 55" panasonic for $350. Brand new, no refurb, in the box. What I did not know is that it will not do 720 i or p. So if a program is shown in 720 what happens. My dvr is set for 1080 only and if I am watching a show in hd and I switch to sd it makes a definate difference in picture even though the show is shown in 720. What is happening here?