Debian 9 and GTX960 : can't use 4k


I use Debian 9 for Kodi (so no desktop, only cli) and i’m having a lot of issues with a gtx 960 and trying to go 4k.
Before, i had a GT430 so limited to 1080p, everything was working fine.
Now, even when i limit the resolution to 1080p, when i exist kodi, i get a black screen, then “no signal” (i usually don’t exit kodi so that’s not my main issue).

Real problem is, i can’t do 3840x2160@60hz. I use drivers 375.39-1.
The TV can handle it (tried on a windows computer).
I got the edid info on windows and tried adding a modeline in the Monitor section, but then i get an error when X start “Modeline Hdisplay expected”.

For kodi to work i have to put Modes “1920x1080”, otherwise i get a black screen (then no signal).
I tried everything i could think of and found no straight answer anywhere.
I even tried xrandr and input the infos, doesn’t work.

Could i have a simple step by step guide on how to make it work ?
My current xorg.conf file with input sections removed

# nvidia-xconfig: X configuration file generated by nvidia-xconfig
# nvidia-xconfig:  version 375.26  (buildd@debian)  Fri Jan 13 02:38:29 UTC 2017

Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0"
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"

Section "Monitor"
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "Unknown"
    HorizSync       28.0 - 33.0
    VertRefresh     43.0 - 72.0
    Option         "DPMS" "false"

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    SubSection     "Display"
        Depth       24
        Modes "1920x1080"

When under kodi, i can select 3840x2160 in the settings, but i get a black screen and no signal message, then it goes back to 1080p.