Overdrive light flashing in 1998 Explorer. Help!

The O/D light has been flashing on and off in my 1998 Explorer for about a week, but was driving fine. Now, it seems to not go into gear as easily. Any suggestions as to what could be causing this?

Have the transmission trouble code read. That should give you a place to start. Otherwise, it's just expensive guesswork.

How can I retrieve the trouble code?

Stop driving it.. The flashing light is a indication of a failure or problem state with the transmission. You will unfortunately need to take it to get it read for transmission codes since unless it flashed or illuminated the CEL (check engine light) a typical OBDII scanner will not read those codes. It could be various things that cause your issue, driving it could further the damage.

Welcome to this forum! The flashing light represents a fault which the PCM has detected within the transmission. The computer will throw the vehicle into FLEM (limp) mode. This will cause the EPC solenoid to allow more pressure to control the various internal parts, but will add additional stress in the process. This is why it's better to not drive when this occurs.