When you change stations, does the TV show you the resolution, IE 1080 or 720?
82" is pretty big, if your local stations are broadcasting at 720, or even low bandwidth 1080 its going to be really visible on such a big screen. What happens if you try a Bluray or Netflix with a 4K resolution
How close are you sitting? For a screen that size you should be 12-15 feet away from the screen, if you're closer than that and its not a 4K source then you're going to see some pixelation.