10 or 15 min begins to produce horizontal lines and distortion

I have a similar issue with my RCA UHD, model RWOSQU5050-B. Details are:

The TV that has a new t-con board and new main board. The picture is perfect for 10 or 15 minutes after turning on, then it begins to produce horizontal lines and distortion in the middle section of the screen. After which it keeps getting worse until I turn it off and let it cool. Any ideas of the cause?

More info to my issue: I tried leaving the TV on to see if there was any change and after 20 minutes the bottom half of the screen was doing some weird things... like going all white, or a half picture that lagged behind the top half of the screen which was not affected (the top half of the screen worked perfectly). It almost clears up and then returns to doing weird things. The top half of the TV is perfectly watchable throughout the 1 hour of watching.