This question would probably be better answered in the thread for your TV or similar Panasonic TVs. I have heard of some firmware updates causing problems with different AV devices so you'll want to check with others to see if anyone has updated their TVs and how it went for them.
As far as your specific problem, the firmware update could help. However, a lot of cable companies tned to move their QAM channels around a lot which causes havoc with QAM tuners. I personally think they do this on purpose in order to frustrate people and convince them to rent a cable box. That could be what is causing this issue, it might not be your TV at all.