Some HD channels have sound,no picture?

I just hooked up my new LG LM7600 tv and I have AT&T Uverse. I have the tv hooked up directly to DVR box via HDMI cable that was purchased from Monoprice.. It's a high speed cable that they suggested to me after I told them my setup being 3d as well.. On certain HD channels I am just getting sound but no picture for several minutes? If I leave it on that channel, after a few minutes the picture will appear. This is only happening on a handful of channels? Does this sound like a problem with cable,tv,or AT&T?

I talked to Monoprice and they said to try another cable to see if it's still an issue.. But you are saying no to it being cable? I really don't want to have to call AT&T again....I have issues with their customer service