Seriously, this is infuriating me. Most of the time, the game will be running smoothly. Then BAM! sudden lag spike where the game seemingly locks up, or just stutters. Sometimes it'll happen when I'm running through the city, other times in the middle of a firefight. Lag spike hits, and I'm dead. Doesn't matter what settings I have, be it high, medium, or low. I can have a two hour play session with hardly a hiccup, or I can boot it up and get into my first firefight, only for the lag to hit.
My specs are AMD FX 6300 six core, Geforce 1060, 8 gigs Ram.
That CPU is pretty ancient by now (and honestly wasn't good for gaming even when it was new), I'm guessing the rest of your system barring the 1060 is severely outdated as well. So I'm guessing there's probably an issue with your system causing it, not internet related lag. Could be a HDD on the way out, temp issues, running out of RAM, etc.