SPRUNG Passenger car trucks are too finely detailed to allow for the stress of shipping. It's because everything on the truck can move..wheels, springs, suspension arms.
The shipping carriers put a LOT of stress on packaging. Lots of Ups/Fed Ex/USPS horror stories.
So I doubt it's a lionel QC inspection issue. Everything gets from China to Lionel palletised. It' when things get shipped to distributors and then locally shipped to your LHS when probably the damage is done.
A simple inspection is to pick up an individual car box and lightly shake it...if it rattles like loose parts..most likely...its got broken truck sideframe parts.
Easy enough warranty fix by your LHS. ...OR contact Lionel for warranty repair
Don't invalidate your 1 year warranty buy trying to repair yourself.
Out of warranty? Bought used?
IF..you have the experience of the disassembly of Lionel heavyweight cars,... truck assemblies are not hard to remove and replace.
If not...seek out someone who does (fellow club member. LHS repair, ).
There is a lot that can get broken. Screws lost, wires disconnected.
If you are out of warranty, for whatever reason, and don't have the funds.....
Passenger car Sprung truck side frames are held on to the assembly by 2 screws. The side frame consists of the sideframe, suspension arms, springs, wheel journals and journal covers..all in one piece.
You do need to remove the body shell, interior, from the frame, and then remove the truck assembly from the car floor/frame to get to the sideframes of the trucks. Really being careful to not break the lighting wires from the truck assembly.
EASY PEASY after a few OOPS.
SO......Lionel needs to stock up on assembled sprung truck sideframes. For those who have to fix their own cars.
AND ...MAYBE
Re access and maybe make the sideframes and suspension parts out of stamped steel similar to the truck assembly body or the floors of the passenger cars.
2 cents worthless