LTO-3 Slow write speeds?

Hi All

Need some assistance in troubleshooting slow write speeds using my HP Ultrium LTO-3. My setup as follows.....

Supermicro server

2 X Xeon 2.0ghz processors

32gig ram

Server 2008 R2

Backup Exec 2012 SP1

HP Ultrium LTO-3 SCSI

LSI Ultra320 SCSI Adapter

My write speed has not been over 120mb /min, I know this drive is capable over 1000mb/min? Have tried using Symantec and HP drivers to no avail?

Any assiatnce would be greatly appreciated.

Dane