I had the identical problem with my Epson 740i when I upgraded from 10.2.8 to 10.3. Apparently the problem still exists with the current upgrade.
The problem is that the required plug-in gets moved to an incorrect location during the upgrade process.
Search your hard drive for "SC740.plugin". Mine shows version 1.2.9. Once located, move it here:
Library/Printers/EPSON/
I would then go into the Utilities folder and copy the Epson Printer Utility to the dock to keep it handy. You should now be set.
You can tell if things are working properly when opening the Epson Printer Utility. If there is color highlight over the "SC740" within that window then all things are go.