World of warcraft lag spikes

Hello,

My internet is flawless except for one game - world of warcraft:

From what I understand, in world of warcraft there are realm servers and instance servers for doing certain kinds of content (dungeons).

I am having a problem with huge lag spikes when playing the instanced content (there are no issues with the open world realm connections).  Connection will be fine and but will randomly spike up to 1000ms.

This issue is not present during the week.  It is present to some degree on Saturday's but is very bad on Sundays.  I may just notice it more given I mostly game on the weekends, but there is a definite difference between saturday and sunday.  I have scoured the game forums for anyone with similar issues - and while there are some there do not seem to be any that have the issue only on certain days of the week.   There is no one else in the house using internet.

I have tried using a VPN to route to different parts of the US with no success.

Any assistance is greatly appreciated.