Slow,slow backups w/Arcserve 6.5

I have a Dell 2400 running Netware 5.0, Archive Python DDS3 tape drive, 27GB RAID 5 array and Arcserve 6.5. My backups start out slow and go down hill from there. I come in the next morning and try to kill the running job and the server abends. I’ve tried Novell’s and Arcserve’s troubleshooting tips but cannot pinpoint the problem. I even got Dell to replace the tape drive but that wasn’t the problem. Any ideas?