88 4Runner O/D flashing...

I have a 4Runner 4x4 EFI 22RE 194000 miles not too long ago it started to skip 2nd gear it goes from 1st into 3rd and the O/D light flashes it runs like that for 15 to 20 minutes and then runs fine it shifts right and runs normal can somebody tell me what is wrong with it help please!!:banghead:

Problem fixed!!(i think) talking to a mechanic that took care of my car before told me to try TUNE UP SEA FOOM FOR AUTOMATIC TRANSMISSIONS the little can costs $27 , I just pour the can after the engine was warm ,drove for 8 miles flushed the transmission fluid and replaced with new fluid its been shifting nice and smooth for the last 3 days (hope stays that way total cost $37 dollars