A:Answer I don't know about Direct TV, but cable TV isn't the best way to fully experience the capabilities of today's 4K televisions. For example, I have Comcast. The best they offer, at least where I am, is 720p. Almost all of their "HD" looks terrible - blurry with bleeding, etc. Over-the-air TV, on the other hand, does not suffer from the bandwidth constraints imposed by cable providers, and the picture is quite visibly superior.
As a test, you may want to hookup an antenna and check out an HD broadcast from one of your local stations. If you see a huge improvement, the problem isn't the TV, it's the source.
Good luck!