[Warner306]

now got it playing for days or no dropped/repeated frames with 4k hdr, bluray and dvd :-)

Warner306 is correct in saying, dont touch the reset gpu button while configuring custom modes.

i also think that changing modes while in the nvidia cp helped as well, also changing to rgb, 12bit and full helped before configuring the custom mode.

also got rid of the sunburnt skin tones by changing the LG tv colour gamut to auto instead of wide, extended.

I take it you disabled color calibration controls in madVR? In that case, madVR would output BT.709. You could try setting the calibration to BT.2020 or DCI-P3 and setting the LG back to wide or extended, but having it convert to BT.709 when SDR content is encountered would be more accurate than upconverting from madVR to DCI-P3. The calibration setting in madVR only effects SDR mode, not HDR passthrough, FYI.