Without being there, I can't fix your dim issue problem, but I can address the other problem. UltraHD Blu-ray discs are encoded at 3840 x 2160, so the lines of resolution you're seeing in the menu is correct. People conflate 4K with UltraHD. They're completely different resolutions. 4K is meant for professional or commercial video, not consumer video like UltraHD Blu-ray is. There are no Blu-ray discs encoded at 4K resolution.What size and screen material are you using? Maybe we can figure out why your image is dim.
Thanks so much your answer was incredibly helpful. I have a 110 inch green, a Studio tech 100 by Stuwart. Before I bought the screen I called up the company and that is what they suggested. It is going to take me until Thursday to put back micro unit which was just upgraded to 4K.