Samsung UN55D8000 Screen Dim

Hello all! I have a Samsung UN55D8000. The screen still works but functions dim, as if someone reduced the brightness setting. The ECO settings are all off which are known to cause this issue.

Also after doing some troubleshooting when I put the TV into 3D Mode, the screen quality and brightness return to perfect operating condition. But when I go back to 2D, the screen is dim again.

Is this the Main Board failing? Or do I need a new T-Con Board?

Any help would be greatly appreciated.