What all comes with the rubicon express 3.5 lift? What all was replaced?
Does it happen over bumps or normal smooth road?
1)I'd start off by checking the trackbar nut and bolt at the frame. Put a wrench on it and see if you can tighten it. See if there is any wear on the frame from the bolt or nut moving.
2)Verify you shocks are tight at the tower "nut up top" look at both sides make sure they look the same meaning the you see the same amount of threads above each nut.
Get under there and put a wrench in everything that was replaced. Mechanics are only human and tend to miss stuff from time to time.
Only on bumps. Like potholes, railroad tracks, expansion joints, etc. Good on smooth pavement. Items replaced were shocks, springs, track bar (front), track bar bracket (rear), front and rear bump stops, sway bar end links and cam bolts.