The router ports should be set to 'duplex full', not auto. Make sure you have your 'cat 5' wires set to 1,2 looped to 3,6. You may also have to beef up the 'buffers' statements to get the ports to run 'wire' speed. I've never tried it, but you may be able to up your MTU's also. You should have identical router config's on both sides for those. A secret tip from me to you: Make your back-to-back cable at least 2 meters long, and see if that improves your packet loss.