Have about 3600 miles on my '06 QC CTD 2500 G56 SLT and have been pleasantly surprised at how well (smooth) it rides for a 3/4 ton... until now! I was out of town yesterday and hit some of the roughest railroad tracks I have ever seen and ever since I have a BAD vibration/hop that seems like is worse in the rear. This is crazy. How could RR tracks do that? They were rough as h@%!!. and I was in a hurry and hit them at about 45mph, felt like the truck was going shake apart, I feel sure the rear tires caught some air. But still! What the heck? I checked and I don't see where any weights fell off anywhere. I feel stupid asking if a (alum) wheel could be warped, but what else could it be?