Same thing here. My ping is a pretty much doubled to what it usually is.

I can roam around freely but when I have to access my gear (combine, use, pick up...) it takes a while to work.

Is there a list of ports that we need to forward? I had no problem with the DayZ mod/ Arma2/ Arma3

Edit: I've just updated my modem's firmware to its latest version and now the ping dropped down to normal levels and no more lag in the inventory :)

Try updating your modem firmware :) Hope it helps