87 YJ Steering problem

I have an 87 YJ with power steering. It has stock size rims and tires (225/75-15 tires).

Lately the steering has become super hard to turn. Its worse than any non-power steering vehicle I have driven. The steering effort really doesn't get better with speed, or course you don't have as much to do...

The peculiar thing is that the steering effort isn't really constant or even constantly increasing as you get toward the lock. Turning from lock to lock there are easy bits and very hard bits. I don't know if its the right way to explain it, but it is almost like turning against a cam. This is true standing still or going slow in a parking lot. Engine speed doesn't seem to matter.

I have checked the power steering fluid and belt. The pump turns. It squeals a little at the locks. One suspicious thing is a slight mechanical moaning sound that can be heard at low speed (crawling up to a stop light), kind of u-joint like, but I am not sure.

How do you go about diagnosing this one?

Thanks