I have the same tv and I believe the same roku. What I have been doing is each day I get the same message, I go and switch to automatic and for whatever reason it reads only 1.4 never 2.2. Then I switch it to 1080 and it is good for a few hours of constant viewing. I then ordered a monster cable from Fry's that was capable of UHD but that still didn't solve the problem. I did open the hdmi port like the manual said to do in the setting for the tv, but still no luck. All I still get is 1.4. Tell me if you get any good results.
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