2003 expedition replaced p/s pump and steering rack. it is still hard to initiate a turn in either direction regardless of speed

First, make sure the PS fluid is not RED.
I hate when mechanics use transmission fluid instead of PS fluid.

Second, make sure you have enough PS fluid in the PS reservoir.
If it's low, then air gets injected into your system, so keep it filled.

Third, exercise your steering (full left & full right) while idling to remove air foam (bubbles) in the system.

Should be good in a day or two.

Raise the truck up and turn the wheels left to right, you most likely have air in the lines.

WARNING BEFORE DOING THIS PROCEDURE BECARE IF YOU HAVE LONG SLEEVES - JEWRELY- LONG HAIR- KEEP IT AWAY FROM DRIVE BELT. YOU NEED TO BLEED POWER STEERING SYSTEM.WITH FRONT WHEELS IN THE STRAIGHT AHEAD POSITION.CHECK POWER STEERING FLUID.IF LOW ADD FLUID UNTIL FLUID REACHES COLD MARK ON THE DIP STICK.START ENGINE RUN IT FAST IDLE.THEN CHECK POWER STEERING FLUID AGAIN.PUT POWER STEERING PUMP COVER CAP BACK ON.WITH ENGINE RUNNING TURN STEERING WHEEL SIDE TO SIDE.WITHOUT HITTING A STOP.THIS WILL WORK AIR OUT OF SYSTEM.KEEP THE RESERVOIR FULL OF FLUID AS THIS IS DONE.WHEN THE AIR IS OUT OF SYSTEM.RETURN THE WHEELS TO THE STRAIGHT AHEAD POSITION.LEAVE VECHICLE RUNNING FOR SEVERAL MINUTES BEFORE SHUTTING OFF VECHICLE.ROAD TEST VECHICLE.MAKE SURE IT FUNCTION CORRECTLY FREE FROM NOISES.