Help with igb driver/nics, strange issue.

I have 3 boxes, each with two nics. One nic for the private network and 
one for the public network.
The private network is all on the same vlan. All 6 nics are on the same 
switch. All connections are 1000tx Full Duplex.

I will call the servers Box A, Box B, and Box C.

When i FTP data between Box A & B i get abou 25MB/sec.
When i FTP data from Box C to Box A or B, i get about 20MB/sec.
When i FTP data from Box A to C i get 10MB/sec
When i FTP data from Box B to C i get 200KB/sec...

Can anyone suggest why i might only be getting 200KB when transfering 
data from Box B to C but not when transferring data from Box A to C?

Thanks in advance!