GMC Repair: steering, pressure valve, steering box

Question
I have a 99 Silverado 1500 ExtCab 4x4.  I noticed an air hissing  sound and difficulty turning to the right, where as turning the wheel left is fine.  Fluid was low so I added more but still it is doing the same thing.  A few months back I had to change the cooler and lines due to a leak.  But it has been working fine.  Is the steering box shot or the pump?? Would it help to maybe flush the system?

Answer
could be a few different things, 1) it could be p/s gear, possible restriction interanlly, 2) the high pressure valve on the bake of the P/S pump could be faulty.  If the gear has come apart internally I would highly reccommend replacing the P/S gear and pump as the debris from the gear could contaminate the pump, the fluid should be thoroughly flushed if you believe the gear has combusted.  If not you will be replacing both parts again in short time