ok, yeah that router should handle alot of traffic, it a classic goodie! Have you scanned for Maleware/spyware? if not try "malwarebytes" its free and a great program! You could try and update to the latest and greatest drivers for the NIC. Or Delete the NIC from device manager, and reinstall it. Or if the NIC is going out it could be sending out massive amounts of traffic.... Just one faulty NIC can create a broadcast storm that can take out an entire network (couple years ago, LAX airport had that issue... some blogs about it:http://www.xtremesystems.org/forums/showthread.php?t=155489http://myindafatigable.blogspot.com/2007/08/20000-people-stranded-for-hours-at-lax.html)
Some things to try/think about... or if you have already tried it Post up and let us know.