Linksys Wired Router :: RVS 4000 Slow Upload Speed?

I am using a Cisco RVS 4000 to test a new 10M/10M internet connection.  I'm having a small problem performing the ISP's speed test (speedtest.cavtel.net).  The download test consistently gives me 10Mbit/s, full speed for the connection, however the upload speed is usually about 5.5 Mbit/s. My ISP has been onsite and has checked the lines and tested directly, and we have determined that if connected directly we can test to full upload speeds, but when the RVS is connected, we cannot get full speed. 
 
 We've tried different cables, reseting to factory defaults, updating firmware, changing port settings, and toggling most of the other setting on the router. Some settings do have a minor effect on the upload speed, but nothing that gets me back up to 10Mbit/s.
 
I did notice that there appears to be no way to set speed and negotiation settings on the WAN port. Perhaps I am missing it, because that seems like a possible culprit.
 
Otherwise, the only only thing I can think of is a warranty return to determine if the unit itself is defective.