So, just as an update in case someone is following or does a search for a similar problem in the future:
In the interest of being 100% transparent, there is a Vizio soundbar in the middle running CEC/ARC so the configuration looks like this:
Media Server ---> Router ----> FireTV2 --18" HDMI--> Vizio SB4051 Soundbar --6' HDMI--> TCL 65R617
I played around a bit more over the last couple of days and it just seems to be that the FireTV2 is the problem.
- I swapped out the 6' HDMI cable even though it functioned fine with the previous TV and there was no change in performance; still dropping frames.
- I did a factory reset to the FireTV 2 and nothing changed: still dropping frames.
- I hooked up my FireTV 3 pendant directly to the TV and connected it to the network via WiFi. It streamed all of my 4k test media perfectly, not a single dropped frame that I could notice. So, now I am finally convinced that the TV itself is OK, thank goodness but now I am wondering if the soundbar is having trouble passing an HDMI 2.0 signal.
- Disconnected the HDMI between the FireTV 2 and the soundbar. Plugged the FireTV pendant directly into the soundbar......... everything worked beautifully.
All signs are pointing to the FireTV 2. I ordered 2 new HDMI cables from Amazon and a new FireTV 4K stick. They should be here tomorrow (Tuesday).
So, the TV is great. With a few calibrations and a little troubleshooting I have the picture looking pretty good and the television seems to be handling motion very well as long as the source is good. It's not plasma good, but the bigger screen, brightness and 4K is worth the penalty.