If you send the same transmittal over and over, for say a subcontract or a change order, you can open an existing transmittal and copy it. It will keep some of the info filled in, so you only have to fill in a few spots. In Project Management, go to Documents, Transmittals.
Open the Transmittal that you wish to copy and click Copy. It will make it use the last number in your series, and copy most of the info. Fill in the info missing and click Save.