Blurry Channels

From the moment I installed the mini-box's I have had problems with blurry channels. I even tried upgrading one of the TV's to a Receiver/DVR hoping the problems would end. Now more than two months later I am still struggling with channels that can never be counted on, and more than 13 tech visits to my home. A new line from the pole to my house has been installed, along with a new line into my house. I am at a loss as to what to do, but really do not want to change to a satellite co. Prior to Cox going all digital I never had any problems with my cable. Does anyone have any suggestions on things I might try, or who I could talk to. More than half the techs have told me the problem is in the line and not in my house, but the problem never gets fixed. Any ideas?