I have a 2002 FF 3.0, I saw somewhere that some rangers use ATF instead of PSF and was wondering how do I know which one to use in mine.

 

For this 2001, for 20+yrs now have used same MerconV compatible ATF in the PowerSteering as whats in the 5r55e Auto Trans.
Routine here is to HandPump 1/4qt from SteeringReservoir then refill with fresh MerconV;
also HandPump 3/4qt of old ATF from Trans DipStickTube then refill with fresh MerconV;
also HandPump BrakeReservoir then refill with fresh DOT4 BrakeFluid;
do this every 4kMiles\6mths & dispose of those fluids along with routine Engin Oil+Filter change.
Use a seperate dedicated HandPump for each different fluid type; store HandPumps in seperate ZipLock bags until next use.