I would do a flush and refill on your PS fluid. To do this, disconnect the return line from the pump. Drain out what comes out from that fitting. Block off the fitting hole in the pump. Direct the return line to a oil drain pan. Fill up the pump, then crank over the motor till it belches out all the PS fluid. Repeat twice to flush out the rack.
Reconnect the return line, and fill the pump. Start the motor and turn back and forth all the way a few times, recheck the fluid level. This should help work out air in the system. If it is still stubborn, you can get a hand vacuum pump and remove the fill cap and pull vacuum on the system while the engine is running. This is a Ford TSB and it was mentioned with the paperwork that came with my rebuild PS pump. I was able to bleed the system without pulling vacuum on my car.
The pump could be ultimately shot, it's kinda a pain to remove, as you can't remove the pump without pulling off the pulley first. Not much room to do it with the radiator still in place.
BTDT