Maybe a wild goose chase or worth considering. At ~180k miles, my Ford Expedition started failing to down shift from 4WD-High to 2WD-High. After much reading, I learned that failing transmission *sensors* can cause the problem, and that disconnecting the battery momentarily can cause the computer to reset things and get back into 2WD. It sounds off the wall, but I had ~4 lockups that were all solved by disconnecting the battery.
My 1988 Toyota 4x4 taught me about binding and backing up, and my Expedition taught me about failing electronics.
--SiletzSpey
