My 2003 Ford Explorer(XLT 4WD) jumped out of OD and will not go back into OD when I push the button. Does anyone know what the problem(s) may be?:

Not to sure with it being newer than an 01 but that can be a sign of the transmission needing service like a shift sylenoid or something, I'd go and have a computer hooked up to it to pull the transmission codes, it should be putting them out if it's having O/D trouble.

check the speed sensor on the tranny

If you do a search on the Explorer forum for "overdrive" you'll find 79 hits (as of 5 minutes ago) and some of them are likely to offer good information related to these issues.

-Rod