While playing Halo 4 on the XBox 360 the TV would turn off randomly every 2 to 8 minutes. I would simply press the power button and it would come back on and stay on for another 2 to 8 minutes.
I contacted Vizio because I could not find the M550SV on the list of firmware downloads. So far they have been worthless with automated replies. I chatted with a representative this morning that informed me that email@example.com aren’t really technicians and the online registration process through the TV doesn’t send the freaking serial number (the first piece of information they ask for every time you call).
Another shameless plug for Just Answer: http://www.justanswer.com/tv-repair/67whx-vizio-model-m550sv-tv-playing-ps3-no-reason.html
I tried this procedure yesterday (although I have read on Fix Ya that the duration to hold the power button is 3 minutes instead of 10 seconds). It stayed up for a couple of hours but rebooted (hopefully and presumably after the firmware update was downloaded and installed automatically). Hopefully it is on until I turn it off now!