I have spent literally days on trying to figure out why one end of the passenger car was so high. The bolsters were the same height relative to the floor and the platforms were not .5 mm different from the floor, but somehow the car was sitting with one end a half millimeter higher than the other. Finally, I switched trucks end for end, and the difference went away.
A few more minutes of puzzling revealed the culprit: the hole in one of the trucks was too tight. So, when I backed it out to allow a little equalization, it was actually lifting the whole car! A few twists of a broach and all was perfect. Still, a strange puzzle.