4K Screen Flicker

Just replaced 4K box again- 

I have a 4K Xfinity box and 4K TV - When I click settings on Xfinity remote -> Device settings -> Video display 

It shows:

- HD = Adjust your video resolution  to 4K UHD content displays at 2160p60

- I have 4K UHD Capability 

- 4K UHD XG1v4 

- 4K UHD SAMSUNG

BUT—if I adjust the video output resolution to anything above the 1080p options, I get intermittent screen flickering. 

Either of the 2 4K options causes this. (4K p30 or 4Kp60(best available))

Of course everything has been refreshed/rebooted/restarted with Xfinity chat. 

This ONLY happens on this tv. Same tv has Xbox that functions in 4K with no issues. 

Ideas?