2004 Ford Focus - overdrive off light

Is your check engine light on? What you are describing sound like the transmission is shifting down to 3rd gear from overdrive randomly. There is an overdrive button (your owners manual will show you its location - usually the end of the gearshift lever) are you hitting that button accidentally? Or possibly that button is failing and triggering the overdrive off when you hit bumps. either way, I suggest that is where the problem lies.