Update:
While still working on the Christmas layout, I have been running these cars on both the 0-36 loop and the 0-48 loop for two weeks now.
I found that I needed to remove the hoses that are attached to the couplers. The hoses that were on the inside of a curve where not leave enough swing room. From time to time I would get a derailment.
The hoses are easily removed there are two holes in the top of the coupler arm that hold the hose unit. I used forceps, but tweezers or a small bladed screwdriver will work. You just need to lift up on the hose unit.
Now I can run them at higher speeds= 40smph.
Mark W.