Have a Nordyne model E2EB. House temperature will not get above 65 degrees, have thermostat set at 70 degrees. Warm air is coming out of all the ceiling ducts. Fans run all the time, but house temperature does not get above 65 degrees. Outside temps are 20 degrees

20 degrees and a wind can keep a house at 65, easy. Your house is just leaking warmth faster than it can get heated.
Do you really have heat coming in at the ceiling? That is poor design, since warm air rises. The rest is insulation, tight windows and doors, wrapped ducts, CLEAN FILTERS, unblocked return vents, and efficient furnace.