As a test, just connect your cable box directly to your antenna input on the tv via coax (disconnecting the HDMI cable). That way, the only cable signal going to your tv is coming from the cable box. Using the internal ATSC tuner, scan for your cable stations. You will have to set your tv to the Cable/Ant input but you should be able to turn on your tv and your cable stations should be there. Now, if the U-verse box is turning itself off sporadically, then that's a U-verse issue which you will need to work out with them. At least you know it's not an issue with your tv. I'm not familiar with placeshifter so I can't help you there. I'd start simple, get that worked out, and then add on devices/components.