I don't know if its just my unusual layout or not, but I find a huge difference in the way rolling stock holds the rails with metal trucks when compared to cars running with plastic trucks. The cars with metal trucks seem to hold the rails far better over rough G brand switches and going up grades going around curves. On the steep grades on my layout, mixing cars with the two types of trucks often causes derailments. I'm now running consists exclusively with metal trucks over the more challenging areas of my layout and cars with plastic trucks where there is smooth perfect nearly level track. This seems to work out. The weight and/or the sprung action of the metal trucks seem to make the cars far better runners. Do your cars with plastic trucks always hold the rails? What say you?