This is the 5R55W transmission behind a 4.6L V-8, and 3.73LS rear end.

Last night we came home from a week in our camper. The camper is light
(3500 pounds) compared to the tow rating of the Explorer (7000 pounds),
but there were a lot of steep grades, and altitudes to about 7000 feet,
so the vehicle was working hard during the week. We kept the OD turned
off at all times using the button at the end of the stalk.

During the trip, we experienced perhaps a dozen hard 4-to-3 downshifts
on steep upgrades at mid-to-3/4 throttle, but not WOT. As we got within
a mile of home, the "OD OFF" light began flashing rapidly. I parked the
camper and turned off the ignition. Restarted it half an hour later, and
the light no longer flashes.

I will take the vehicle to my mechanic (who is not a Ford dealer) later
today, but in the meantime, can anyone tell me what I should expect to
find? In particular, what does the flashing OD OFF light mean?

Thanks

Bill Jeffrey