All of my new Lionel 21" passenger cars are beginning to have the couplers pitch upward as the pull and weight of the heavy cars gradually bend the coupler post on the Kinematic plate.
The rising couplers damaged the Diaphragm on my Amtrak Dining Car. The Up Excursion car couplers are all moving upward. My Southern Pacific cars with the Full Diaphragm are also doing it, though the Full Diaphragm keeps the bending from being noticed as much.
My C&O, NYC, and Wabash cars from the first-run did not show this trait because they have Full Diaphragms. They were probably doing it, but I did not notice because of the Full Diaphragm. The couplers rub on the plastic bottom of the Full Diaphragm, keeping them from raising more. I am not happy because I have already detailed all of these cars with painted Preiser people.
The metal chassis of the 21" passenger cars is heavier than the 89' Auto Carrier and 86' Box cars. The extra weight gives a little more of a tug as the kinematic couplers when they swing side to side and the centering spring bungee cords the cars occasionally.
I ran three of my UP cars with seven of the Southern Pacific cars to see the length of the Pennsylvania Broadway Limited I ordered. Ten cars will create a lot of pull on the coupler posts where they join the Kinematic Plate.
The photos may be blurred because the train was moving forward to put a load on the couplers.