I agree with Brakie. With that many problems I would guess the bottom frame is not fitting nicely into the body shell and is bending down on the ends for some reason. I can only speak for the Athearn and Accurail cars, I don’t believe I have any ConCor. In 40 years and thousands of examples I’ve not seen the trouble you speak of. I have found that an Athearn blue box generally needs 1 red (0.015") Kadee washer per bolster. The exception is the ice reefers that generally need two black (0.010") Kadee washers. The one huge problem with Athearn cars are the tanks. The tank cars do not have the metal snap on boxes and the plastic “cover” will eventually sag. To solve that I wrap the end of the coupler box with some thin wire.
I have found that some of the Athearn BB cars underframes can cause the couplers to droop because the underframe is flexible . The solution that I have found is to epoxy the coupler box to to the underfloor weight or plastic cement the the coupler box where it meets the bottom of the end of the car.this keeps the coupler box straight and level .
You know what I find odd, that people here have number 5’s in Blue Box Cars that are the correct height with no washers. What I have found is 90% of my BB cars one end height might work with a #5 and the other end will sit to low. Most of the time I use a raised shank coupler to correct the height.
Ken
Ken,I have never found the need to use a high or low shank coupler on any of my BB cars since 90% of the time the frame or weight was warp and in some odd cases the floor was badly warp.
I simply straighten the offending piece and that solved the problem…
One more thing I will share is my last BB covered hopper kit the bottom was warp! I had to straighten the floor before the couplers would match the KD coupler height gauge.