Quote: Originally Posted by ultralame
I am ready to get a new network adapter, but I was hoping that wasn't necessary.
I've built 3 PCs in the last several years, and each/every one of them has had the on-board Gigabit ethernet port die! Most recently, I too was having peculiar network problems, first noticed because I keep my Firefox profile on a network NAS. Long story short: from the suspect PC I did a "ping <another Gigabit device> -t" and observed that I was getting failures around 5% of the time! I put-in a gigabit NIC and all is well again.
So you might check that your pinging is perfect; another very nice tool is Ixia's Qcheck (though you need its software on another machine to check thruput against).
I know you said it's a new mobo, but cable and NIC are always things to check.