When you press a form feed on the new printer, does it eject 7" or 11"? If it spits out 11", then there sometimes are settings/changes you have to make on the printer itself - not just software or printer driver changes.

Can you preview an invoice rather than printing? If so, does the paper size appear to be 7" long or 11" - ie is the length shorter or longer than the width? If the preview appears to be 7" long (length shorter than width), this means that the software side is dealing with the paper length properly, and the 11" page ejection is more 'hardware' related to settings.