Can I pay additional principal with my Autopay?

Yes. Additional principal payments can be drafted on each draft along with your regular payment. 

You can also schedule a one-time principal payment after your regular draft by visiting the Make a Payment section under Payment. The amount will automatically draft from your bank account. You can also make additional principal payments by check. You can mail a mortgage or HELOC additional principal payment to the  processing center listed below:

Payment Processing
PO Box 660093
Dallas, TX 75266-0093