had this issue 2-3 years ago
turned out to be my Scientific Atlanta EPC2100 REVISION (1) that was causing the issue
couldnt cope with the traffic..
infact even if i opened utorrent or bit commet and left it for 5 mins with NOTHING downloading
it would still lock up my browsing..
i was using a router too... turned out it was the modem..
got it changed for a motorolla and all of a sudden things were hunkeh dorreh