Walthers Budd car issues

[Green_Elite_Cab]

In my rush to get my trains up and running for my club's trainshow, i've noticed an increasingly irratating problem. the Bud cars in my train, specifically a grill diner and a Dorm/lounge car, tend to jump the tracks repeatedly in the same places, but i cannot see the problem.

There are no obvious dips, gaps, or other track issues i can see (usually derailments happen in the middle of flex track).

the dorm lounge tends to derail near the top of a long nearly 4% grade, and there are no gaps in this spot. it is ALWAYS the rear axle of the truck on the "forward" end of the car (relative to train movement). If i flip the car around, this seems to be temporarily negated.

I've tried to adjust the truck tightness/loosness, but the situation never changes, no matter how i make the cars go.

THe grill diner tends to also derail on a curve, but only on a section of level track. while there is a grade ahead, the grill diner is nowhere near it. Once again, i see it just jump in about the same spot.

the only solution to either seems to be to remove cars. The dorm car will always derail on that spot if there is more than 2 (of 4) coaches on the train, but it is unnacceptable to remove those cars. Right now, i've removed the dorm car, MHC, and Express Boxcar that was part of the train, and that seems to have resolved any issues with the rest of the train. Still, i do not understand what the problem might be, and i'd like to run the full train.