I'm usually more suspicious of mechanics when they start wanting to replace things. Check your ball joints for yourself. If you watch this video, Planman takes you right through how to check all aspects of the steering system. The steering boxes for JK's are notorious for a clunk.
https://www.jk-forum.com/forums/jk-w...obbles-260145/

 

The sector shaft is the shaft that comes out of the bottom of the steering box and connects to the pitman arm. It's a common issue with the JK....the sterring boxes are a big POS.

 

I replaced the ball joints with Napa lifetime warranty units. Much better feeling but there is still some. I may try more grease in the steering shaft.