If you don't want to just throw parts at the car you'll have to spend a little time and effort to isolate the problem--and that could be one or more.
First be sure the p/s drive belt is at the correct tension. Fluid up to level. Look at the steering shaft joints--any sign of rust? Jack up the front (safe jack stands, of course) and look at the ball joints for signs of rust. Run the car with the wheels up and take note of the effort to turn the steering wheel. Disconnect the tie rods--feel the effort to turn the free struts--try the p/s. If the strut pivot points are good but the p/s effort remains high you may want to disconnect at least one of the shaft u-joints. It's just not very likely that a p/s rack would loose power without severe leaking. The pumps are very reliable. Frozen joints happen. -- Dave