It made the car have probably 2-3 degrees of neg camber and for that kind of weight for those kind of miles, you were peeling rubber like a banana. The nature of the suspension is such that you are going to have neg. camber if you load down the rear. That's can be by either pulling/towing a trailer or by having a rather large dead body in the truck(dont ask how I know
:p
) Anyway, neg camber is usually adjust by correcting for toe. Or you could install a set of KMAC rear camber adjustment bushings. Then as you load the ol girl up, you could dial in a bit of positive camber till she was straight and then dial it down after the wekend.... Or you could just sell it and get a 500E, an S class or other model that has hydraulic or air self leveling