In regards to the OP, can you supply me with the complete log during one of these events? Should be mostly Info priority, but make sure you go through it and remove any personal info. (Public IP's, MAC's, etc). I think the answer will lie there.
It sounds like the heavy UDP traffic is lagging all other traffic. Question is why. Here are just a few things to try. I will have more idea once you give us some log data.
Basic > Internet > Manually configure > Uncheck Unicasting.
Advanced > Advanced Network > Check off "Enable Multicast Streams"
Advanced > Gamefuel > Disable Gamefuel. (For testing purposes)
PS. Great article here. http://www.isoc.org/INET97/proceedings/F3/F3_1.HTM
PPS. D-link, want me to find you a better HTML tagging system?