You didn't mention if your Explorer has an automatic or standard shift type transmission, If it is an automatic check the transmission dipstick fluid level first. A low fluid level could cause this problem. Check the dip stick level after warm up and If the fluid level is low bring the level up to or slightly above the add mark line on the dip stick (Make sure that you get the correct approved type of fluid) while checking the level take a whiff of the dip stick. A burned smell and a dark brown color would not be a good sign. At any rate you should get in touch with a reliable transmission shop and have it checked.
If you have a standard type transmission you could have either a transmission or a clutch problem.
Again get it checked by a reputable transmission repair shop.


