I have no idea of the root cause but an easy way to root out weather or not the TV is the problem would be to simply swap another TV to that spot for a while. Best guess on what you describe is that it's a signal problem vs a TV problem though.
I'm not familiar with Uverse but I see it is AT&T's Internet based bundle, phone, TV, I'net etc.
Therefore, I would ask, how does the signal get to this particular TV? Does it traverse your home LAN to get to this particular "Box" or does the one box feed all TVs via more traditional cabling after that? If the LAN, this opens up a whole long list of possible trouble areas to double check.
If you can paint a better picture of how it is all hokked up, I can maybe throw some suggestions, but likely nothing revolutionary.
