Asus GTX770 & Dell 4k

[LittlePaul]

Hi,
i have a Mac Pro with a Asus GTX770 2Gb.
I by a new monitor Dell 24 4k, but i have another a Asus VK278.
If i connect the Dell with the Asus (1920*1080 60Hz) the resolution of the Dell is 1920*1080 30Hz!???
I hope that single monitor can view whit his resolution...

Another question:
is i use only the Dell the resolution is ok , but frequency is at 30Hz.
The port enables is DP 1.2

I need help!



Max

P.S.
I have update the driver Cuda and now the resolution is ok, but the refresh is 30Hz!
Why...