O.K. You mentioned 2 months ago, so you really meant 2 weeks ago. I think Costco has a 90 day return/exchange policy on TV's, so you are fine for a while.
Handshake issue is basically issues with the HDMI making a "handshake" between the 2 devices.. In this case the TV and PS3 and TV and cable box. Video/audio drop outs or no screen are the symptoms. You can try unplugging everything for about 10 minutes or so. The turn on the TV and then the device. If you still are having issues with both devices, I would return the TV.