U-Dawg

My 95 F-150, has the 302 with the three speed/od tranny. The issue I am having, sometimes itll shift like its suppose to, other times it'll shift at different times and it'll be in third gear before 20 mph. I know when it shifts right it doesn't go into third until 30-40 mph. And when its shifting wrong it takes a long time to get to speed. Could it be I just need a fluid and filter change or maybe solenoid is bad.