Might consider using TSM Client Instrumentation to see where it is spending most of its time; described in "TSM Performance Tuning Guide."
Another "sanity check" would be to ask yourself: if it wasn't a backup, just any old file transfer, would I really expect this system to utilize 100% of the network? Often the answer is no, even if you don't include the overhead of the TSM Client scanning the 95% to 98% of the files that *don't* get backed up. Just points to ponder....
Best Regards,
Robert Luehrs