I had that sag to the rear as well. Went to the bone yard, saw some low mileage rear rotors (the resurface marks could still be seen) and pads on an Olds Intrigue that led me to the struts and springs. Put the parts on the GP this past weekend, no more sag, even with a trunk full of various tools and a hydraulic jack. Great find....can't beat $15 for a rear brake job.