Hard steering at slow speeds

Has anyone encountered a hard steering situation at slow speeds after the vehicle is warmed up. It seems to me the power steering fluid is being airated as the stiffness is accompanied by a whine. Also does anyone know of the pulley swap for increasing power steering fluid flow at idle. Are the XJ's very particular on the type of PS fluid used? Thanks to all replies.

Best bet is to first make sure your steering pump is working correcctly. Have you been hearing whining? Does it have enough fluid? I did experience similar sensations when my steering pump went. It dumped all the oil on a boat launch and I still wait to see if DEP will hang me for it. next approach is the gear boxafter that.