Learned something new tonight, so here's my second helpful post on streaming issues.
I had my Vizio VIA working perfectly up until a couple of weeks ago when I switched ISP from Time Warner to ATT UVerse. With ATT Uverse, I have my ATT router set to DMZ mode and connected to my Linksys router because it's dual-band and Wireless N (just a much better router).
After the ISP switch, my Vizio VIA continued working for simple data information - weather, Twitter, Facebook, Netflix information, etc. However, all of the actual streaming functions either halted completely or took FOREVER to load such as Netflix (actual movie watching - not searching titles), Pandora, TuneIn Radio, etc.
I couldn't figure it out. I have all of the ports opened that are necessary for the TV. I even switched the TV's IP address to DMZ mode and still failed. I tried uninstalling and reinstalling the apps. I tried updating my router firmware. I tried factory resetting the TV. Nothing worked. However, my two Roku devices were still streaming Netflix and Pandora perfectly. What's the deal???
I figured it out tonight. I was using OpenDNS as my default DNS servers before. The automatic DHCP function on the TV just retrieves the default DNS servers from your router. I went into the TV and turned off automatic DHCP. I then changed the default DNS servers to the Google DNS servers which are 188.8.131.52 and 184.108.40.206. PRESTO! Everything is working like a champ now. Streaming is back to normal (almost instant).
I really don't understand why it would matter but there is some funny combination of ATT Uverse with OpenDNS that the Vizio VIA does not like, but it did not impede the Roku devices from working. The Google DNS servers work perfect with Vizio VIA and ATT Uverse. I don't know if this is a problem with other ISPs, but if you're having trouble with streaming on your Vizio VIA, you might give a try to switching your DNS servers to Google (or something else).
Hope this helps someone.