Nvidia: top resolution not detected

I've got a monitor which can do 3840x2160 & NVidia Quadro P400 GPU. OS: Debian testing. When I try using the official NVidia driver (v. 525.147.95), everything works, but the top resolution is not detected ( in the list in NVIDIA Settings, the highest detected resolution is 1920x1080 and that's what the driver uses) When I try using the Nouveau driver - if I connect the whole setup to a monitor which can only do 1920x1080, it works all right. If I connect it to my main one which can do 3840x2160 and reboot, all I can see post BIOS & GRUB is a brief output from the kernel booting, and then a black screen - Nouveau probably crashes somewhere. Question: how to either - figure out (and fix!) the crash in Nouveau (in particular, where do I find logs?) - or: convince the NVidia driver to detect (and use!) 3840x2160 ? EDIT: xrandr output:

Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
DP-0 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 700mm x 390mm
   1920x1080     60.00*+  59.94    50.00    60.00    50.04  
   1680x1050     59.95  
   1600x900      60.00  
   1440x900      59.90    59.89  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1280x720      60.00    59.94    50.00  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       59.94  
   640x480       75.00    59.94    59.93  
DP-4 disconnected (normal left inverted right x axis y axis)
DP-5 disconnected (normal left inverted right x axis y axis)

when I try to manually add the 3840x2160 mode using xrandr, I get 'BadMatch' error:

> cvt 3840 2160
# 3840x2160 59.98 Hz (CVT 8.29M9) hsync: 134.18 kHz; pclk: 712.75 MHz
Modeline "3840x2160_60.00"  712.75  3840 4160 4576 5312  2160 2163 2168 2237 -hsync +vsync

> xrandr --newmode "3840x2160_60.00"  712.75  3840 4160 4576 5312  2160 2163 2168 2237 -hsync +vsync

> xrandr --addmode DP-3 3840x2160_60.00
X Error of failed request:  BadMatch (invalid parameter attributes)
  Major opcode of failed request:  140 (RANDR)
  Minor opcode of failed request:  18 (RRAddOutputMode)
  Serial number of failed request:  39
  Current serial number in output stream:  40