Samsung C24FG70 72Hz issue

Hi all!

I have a Samsung C24FG70 monitor (144Hz max).
I would like to do a 1080p 72Hz custom resolution, but I have an issue.

I can set 4 different refresh rates from the monitors OSD: 60, 100, 120, 144 Hz.

The "standard" 72Hz timings don't work, it cause frame skipping.
[Image: http://kepkezelo.com/images/mleewqeg7e6fa945h8kv.png]

I set the monitor to 144Hz in the OSD, looked at the timings in the nVidia control panel,
(Horizontal front porch: 48, sync width: 32, total: 2080pixels, +
vertical front porch: 3, sync width: 5, total: 1157pixels, -)
and used them for 72Hz. And it works.
I checked frame skipping at http://www.testufo.com, and voila, no skipping.

But when I play some game, I notice something unusual. It seems like a persistent, very slight stuttering. It's similar to half the fps of the refresh rate. When I look at the data in the OSD, it seems data are correct (72 Hz, 83,3KHz), but I can notice that slight stuttering when playing (though the game can handle 72 Hz, no problem with 72 fps).

What can be the problem?

Thanks for the answers!