Does Your computer respond to ping (ICMP) requests at all?
Some firewalls keep this disabled by default (and for a good reason so).
If this is the cause (the engine seems to tolerate ping delays to a certain threshold only?) try enabling the (few) serves for all ICMP?
Besides that, all game-play traffic is made of (sometimes) huge UDP packages, which might (more often than not) get fragmented and those fragments may arrive out of order causing further delay (lag shield-ing
) that leads to so called rubber-banding (?). If the delays get too large, the server kicks the offending client for excessive "red-X".
Lagging can reportedly be alleviated by the receiving modem - better vendors (U.S.A. made?) seem to be able to combat huge UDP packet fragmentation better than some other (Asian? cheaper?) competitors.
TL;DR:If any firewall (on either PC and ISP modem/router) isn't the cause, try get the modem swapped by the ISP?