i had a problem similar to that with a 4x4 silverado i used to own..only it was the drivers seat that was doing it..i left the red light to hard one day and it went 'bang' and my seat got loose as hell...come to find out...chevy did (censored) work on the frame of those seats...check were the seat frame is attached to the bottom of the seat itself...look any kind of cracks in the frame...my mechanic fixed my in about 30min with a wire-feed welder...all i had to do was by him lunch....look for cracks....that sounds like its fixing to break...
