what picture setting are you using? standard, configured, configured dark, vivid, user? vivid seemed a bit jittery to me so i use configured for sports and normal for TV.
Also i did upgrade my HDMI cables when i went from my samsung LED to this 4k. Depending on your service provider buying true 4k capable HDMI's made a big difference. Time warner picture isnt great but they have poor signals, xbox one looks amazing and even apple tv at 720 is much improved.