What did Boeing improve on the B747-400ER or the freighter version that made it more efficient than the?

Question

B747-400 and its freighter version

Answer 1

Relative to the -400, the -400ER added increased takeoff weight capability and auxiliary fuel tanks in the belly.  The passenger version also offered some interior upgrades.

Answer 2

Increased fuel capacity, EFIS panel, winglets, and upgraded engines with more efficiency, aside from that the interior boasts the high speed container package with individual modules, also honeycomb structures were incorporated to increase forward cabin area and improved strength. Qantas Airways uses the 747-400ER on their L.A. to Sydney routes...