Another possibility might be excessive packet loss, leading to retransmissions. Such packet loss can occur anywhere. It could be network side, or your connection to the DSLAM, but one strong possibility would be packet loss within your home network.
Within the home network, I have twice observed early symptoms of dying hardware (one a switch, another a router, both Netgear 'budget' items) were high rates of retransmissions. I'm not a gamer, but watching recorded TV would stutter and freeze momentarily, which is obviously similar.
I'm not suggesting you go out and buy a new router or switch, it's far too much of a long shot to justify such expense. But if you had a different router you could try, and maybe without the switch, it might be worth the experiment?
Might also be worth swapping Ethernet cables around in case one is dodgy.
I'm assuming you are not using WiFi, else I'd be saying 'try it without WiFi'.