Hi Bro, sorry for delay.
My specs: Win 7 Pro (64bit), GTX 980ti, CPU i5 2500, 8 gig Ram, Monitor Res 1920x1080. Piplay 1.2.95 FW 265
1- Pimax 4K on, Piplay video mode.
2- Right Click; Nvidia control panel; 3D settings; Disable Nvidia DSR
3- Nvidia control panel; change resolution; Customize.
4- Add custom resolution.
5- Add custom resolution TAB with default resolution.
6- Change; horizontal pixels 3840, vertical pixels 2160. Leave all other settings as you see in pic.
7- Press Test and save the new custom resolution.
8- Now in custom TAB, you should see the new custom resolution added. Close nvidia control panel..
9- Go to windows resolution panel, and you should see the new resolution (3840x2160) added. Select and apply it.
10- Custom resolution applied it.
11- Also added 5K resolution but did not work.
All the uploaded pics are actually print screen shots. So pics resolutions are monitor (1920x1080) plus Pimax 4K resolution.
I tried this method with my playing laptop that has GTX 880M 8 gig (Kepler)and did not work.
I have not tried it in Pimax mode.
Please feed back.