Ive tried all firmwares out and never had sync issues etc and im using one of the first hdmi cables out back then has been replaced with a Audioquest Pearl a while back ....... But im on 1080p panel . If Changing from Auto to your specific resolution dont work have you changed hdmi from 1.3 to Hdmi 2.0 in your settings ? Note any firmware updates should always be followed by unpluging unit from the mains for a few seconds . It does help Maybe not your hdmi handshake issue but for updates you should .