I changed mine just over 30,000 miles, 2003 E-450 with 4R100. It needed changing, was getting pretty burnt looking. Ford dealer used a new spec Mercon. Per manual, 30k was change interval for that model year, that application.
I changed it about same mileage on a 2001 Ranger with M5OD manual. Change interval was supposed to be 50,000, but the synchronizers were starting to be stiff. Ford dealer replaced the Mercon with a new synthetic gear oil, told me they don't put Mercon in that manual transmission any longer. Shifting slick, better than my Honda Fit.
