According to information at Epson's website, your ET-2760 is capable of duplex printing depending on the paper stock you are using). If you are using 'cover stock' or other paper of heavier weight than standard '20 pound bond,' you may have to use the manual feed slot.
Are you 'feeding the page in again' on the same path as it took the first time?
Are you ensuring that the printer 'knows' where the paper starts? With similar print jobs using my Epson, I generally make sure the side guides are giving the paper very little opportunity to move left or right, but are not tight enough against page edges to cause drag.
When I'm inserting each page I wait 'til the printer has grabbed and adjusted the starting position of the paper before going back to the computer as pressing the Print button.
Regards,
Barry