Check your duplex. I have had two recent problems with duplex:
One, with a Cisco router - it auto-negotiated every time to half duplex, even
though it really -was- full. Use mii-tool to find out.
Two, with a RR modem - the speed was forced to 10mb half duplex instead of
100mb full duplex. All sorts of strange loss. Once I put it back, all was well.
I have used TONs of 8139s, and while I do see where they are not the fastest
kid on the block, I cannot say I've seen packet loss.
Bob