yeah.. these things are hard to track down sometimes, especially with how communications work with XIV. Your session is relying on a connection servers in Canada and Japan--not only just your system, but those servers are having to synch in the background as well. There are a few things you can try though, just to see if maybe you need to contact your ISP to get involved.

IF you are using wireless. STOP for a while. Run an ethernet cable directly to the router for a while and see if it improves. Wireless is prone to fragmentation, interference, ... all kinds of things that can interject lag. Even something as stupid as being too close to these CFL lights, or having overhead fluorescent light fixtures between you and your router can create problems. I once worked with TWC on tracking a problem down on business cable, only to find out it was a bad transformer on the pole outside causing problems.

On that same note, if you are running a router, try bypassing the router and connecting directly to your modem. I know, it kicks everyone else off the network for a bit--but there is a reason. Sometimes the router can be flaking out. This is more common when you are using Wi-Fi alot, especially in the hotter regions. As the capacitors dry out over time, voltages get skewed and it messes with signalling and such.

If you have a laptop/PC, and are familiar with using netstat, ping, and tracert, you can monitor your connections while logging in and playing to get the IP addresses of the servers it is connecting to. They should fall within two subnets: 199.91.189.XXX and 124.150.157.XXX (the 199 group is CA, 124 group is JP). You can then run ping/tracert to them to see how stable your path to them is. If you spot problems, you can forward your logs to your ISP so they can investigate.

Alternatively, you can just go to speedtest.net and drag the map to find servers in Montreal and Tokyo (where the servers physically reside) to get a rough idea on the quality of the path to those regions. If you see the speed and/or graph jumping up and down with big spikes (a little jitter is normal, but not a down speed jumping all over between 3MB to 16 MB, or an up speed bouncing around from 256kb to 1Mb and back to 300kb). If it isn't fairly steady throughout the test, there may be something going on and you might want to contact your ISP.

I know it sounds weird, considering you don't seem to be having issues with websites and all... but they use a different transmission protocol that puts safeguards in there to make sure the data is delivered in a timely fashion and in proper order. The game uses a protocol without such checks and balances... if the data gets there all is well, if packets get lost/delayed, there is no recovery at all and you just have to wait for the next push/pull to go through and then the game jumps to synch up. Sounds a bit like what you are experiencing.