2001 3.5 super ride shifting?

Installed a 3.5 super ride with rear springs, everything seems to be tight but now when i start/apply the gas and when i come to a stop there is a sound coming from the rear end as if the body is shifting? Anyone else had this and how to fix?

Start with the upper shock mounts. Make sure they are tight and not sliding back and forth on the bar pin. Make sure the U-bolts are on right and tight. Any noise on mine has always been a warning that I needed to tighten the u-bolts more. They do stretch.