Freezing TV

This has been an ongoing issue for months now.  I have 3 TV's in the house.  One has the primary box and the other two have the satellite boxes.  One of these satellite boxes constantly freezes the TV picture.  It'll pixelate, then freeze itself for a second of two, then resume.  Super annoying.  Does it with the other boxes maybe once every hour or so, which I guess is tolerable.  This is one it's not.  

I've replaced this box 3 times now.  Have unplugged, rebooted it, rebooted the router, all the stuff ATT says to do.  Wifi seems to be fine in that part of the house.  Still no dice.  What is wrong with this system?