The HD lowend at Netflix is... https://help.netflix.com/en/node/306 5 megabits. So your numbers are fine.
I see most of what folk and techs do but did you check the date and time on all things? Router, TV, and what else?
And did you set the DNS to 8.8.8.8 on all things?
If this fails, there have been web pages about Comcast throttling video over the net. Nothing I can add there.
At first I thought it was Comcast failing to provide adequate bandspeed, but using Speednet with my iPhone I'm getting 40-50 mbps at my Vizio M55-C2. However, I only get 7-17 mbps (converted numbers) at the TV when it recommended a minimum of 12 (1.5 mbps per Vizio). Thus, there're occasional stutters when using my Apple TV to watch streaming TV. Searching the net for answers reveals scores of others with similar problems despite following Vizio tech directions to reset the TV, resetting router, moving the router, etc. In my case, using a power line adapter (TL-WPA4220), I have band speeds hovering around 40-50 mbps, but this is not reflected on my Vizio TV which shows values of <1 mbps to 2.2 mbps, converted to Speednet values of 7-17 mbps. Turns out this Vizio TV can't be too smart after all. Bummer.

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