@THE_ROONDAWG 

I have a similar problem.  My Cox is 170 Mbps, but the X60 is only handing out 10 Mbps connections.  I've tried 3 phones and computers, connected to the master hub and all the satellites.  Same throughput.  It makes my Samsung 4K TV buffer too, so it's less likely to be your Vizio.  

I'd suggest running speedtests from your phone/computer, to verify the X60 is actually handing out your 300 Mbps, and it isn't dying in the router. 

@mcnt ran a speed test on my iphone from the same satellite hub the TV is connected too, running in the high 200's of a 300mbps connection which makes sense for it being a non-backhauled unit and while others are drawing bandwidth.  We had Vizio replace the main board, saw some improvement with the playback.  I watch the app while streaming a 4k HDR clip and it pulls about 30-35mbps.  Guessing there is more to this than just bandwidth and signal processing.... 

I did notice on the TP link app the TV is only connecting via the 2.4g signal and not 5g....a soft reboot fixes this but, it then reverts back a short time later....will end up running a RJ45 from the hub to the tv for haha's....

Aside from these "issues", for an out of the box solution with very little setup, its a nice improvement from what we had before.  Would still like to see the app improvements and some more info on potentially getting closer to my full connection speed on the satellite units. Backhauling is only an option between the main unit and one of the two satellites.