1999 Ford Explorer Hard 2-3 shift O/D light flashing

After driving about 4 miles the overdrive light starts flashing and it has a hard 2-3 shift. At a stop sign I have to shift to neutral and then back to drive to get it in to low gear. It does help to lock out the overdrive when I first start driving it. I have never changed the fluid. Do you think changing the fluid will help?
thanks warnercl