Having a similar problem with the wife's '00 (it is 2wd) when you would turn close to the block especially to the left there would be a noticeable "clunk" (only one). I had the wife turn it block to block while I watched, saw the top a-frame for the drivers side wheel was moving slightly when it would approach the stop. Further investigation with the wheel off I found the bolts that hold top a-frame to the bracket were loose and allowing the a-frame to slide in the bolt slots.
I am guess it will need an alignment now also since it was allowing movement, I tightened the nuts up and no more clunking.