@ic1 this is not a T-con board issue. Check your video and watch the fade on the left side. "like a black blotch floating across screen" The T-con board can't do that. You can check the video processor on your main board and see if that gets hot. Also, check all the ribbon cables for corrosion and tears. After that, check the "long, skinny boards" that connect to the LCD panel. Those are the driver (scaler) boards. Check for bad cables, corrosion, tears, burned or missing components. Be careful around those boards. they are not replaceable by a DIY'er and only connect via those "flimsy" ribbon cables.
Try to keep the back cover open and have a fan etc. blow some "colder" air across the boards. See if that keeps the TV either running longer before this comes back or if it makes no difference at all.