Slow backups

I have a DLT VS80 1/8 Autoloader.
Every thing seemed to work fine and at a resonable rate. Last week everything backed up slower than usual.
Spoke to Veritas – No help
Spoke to Microsoft – Got credit?
Spoke to HP – Exchanged HW device.
Installed the device and backed up everything with about 181MB/min speed. Except the Exchange Server, everytime I connect and try to back up a mailbox, or even a single message, I get a throughput of 25MB/min.
How is that possible, cause I’m stumbed.