Bob, you are probably correct.  Since I returned the loco to the dealer, I can't really check to see if filing will correct the problem.  Diesel engines have no problems running on the track, but of course they don't have trucks with no weight on them.  Since I want to change over to steam, I think I am going to start over with new benchwork and go to flex track.

Pony trucks going forward and the trailing trucks in reverse.  In all cases it was coming out of a curve.

There were no foam packing pads.

You're probably right about the radius.  Mine is 18".  However, I'm sure I read somewhere that the loco was supposed to be able to handle the 18" radius.

I bought a DCC Sound-Equipped K4 4-6-2 Pacific (item number 84403) today and tried to run it on my small layout which uses Atlas True Track.  The engine kept derailing, so I returned it to the store where I bought it.  The sales person told me that I was the second person to say that there were problems trying to run the engine on track with integrated ballast.  Anyone have any thoughts?