LG 34" Ultrawide 5k resolution issues with iMac Pro

[SCMedic]

I'm having a hard time finding the correct settings/resolution for this combo. Either the ultra wide is letter boxed, or stretched, or the text is fuzzy. Or it's too dim even with the brightness on the monitor turned all the way up. HELP!

And I am aware of holding option while clicking through display resolutions to enable all options. It's currently connected via USB-C/Thunderbolt.

Thanks!

 

[joevt]

What's the model number of the display?

 

[SCMedic]

What's the model number of the display?

LG 34WK95U-W​

 

[joevt]

Get AGDCDiagnose output for each connection type:
1) Thunderbolt
2) DisplayPort

repeat for each DisplayPort version (disconnect and reconnect the display after changing the mode):
1) DisplayPort 1.2
2) DisplayPort 1.4

so there should be four AGDCDiagnose output files (use a different file name for each). Zip them and post here so we can see how the display is connecting to your iMac.
/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_LG5K2K_Thunderbolt_DP1.2.txt 2>&1

 

[SCMedic]

Get AGDCDiagnose output for each connection type:
1) Thunderbolt
2) DisplayPort

repeat for each DisplayPort version (disconnect and reconnect the display after changing the mode):
1) DisplayPort 1.2
2) DisplayPort 1.4

so there should be four AGDCDiagnose output files (use a different file name for each). Zip them and post here so we can see how the display is connecting to your iMac.
/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_LG5K2K_Thunderbolt_DP1.2.txt 2>&1

Thank you for being willing to help. I ran the acdiagnose and got the terminal output, but I'm unsure how to save and zip it so it's helpful for you. Also, do I just run that same script over and over with the LG plugged in and configured different ways?

 

[SCMedic]

Get AGDCDiagnose output for each connection type:
1) Thunderbolt
2) DisplayPort

repeat for each DisplayPort version (disconnect and reconnect the display after changing the mode):
1) DisplayPort 1.2
2) DisplayPort 1.4

so there should be four AGDCDiagnose output files (use a different file name for each). Zip them and post here so we can see how the display is connecting to your iMac.
/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_LG5K2K_Thunderbolt_DP1.2.txt 2>&1

Interestingly swapping to the USB-C to Display Port cable fixed any issues I was having. The part that I find odd is Thunderbolt was working great for months. Oh well.

 

[joevt]

Thunderbolt is weird with this display - it can use a single DisplayPort 1.4 connection or dual DisplayPort 1.2 connections. I'm not sure if the iMac Pro supports DisplayPort 1.4 or not. It has an Alpine Ridge Thunderbolt controller which only supports DisplayPort 1.2, but maybe Apple added a workaround to bypass the Thunderbolt controller for direct connect displays (when you use a USB-C adapter instead of a Thunderbolt dock or Thunderbolt connection). The AGDCDiagnose will tell us how it's connecting. Do you see the HDR option in the Displays preferences panel? I think that requires a DisplayPort 1.4 connection or a dual DisplayPort 1.2 connection.