I just purchased my 2nd 44 tonner, and I noticed some differences between them with regard to the trucks. One loco has 5 gears visible on the bottom of the trucks, and is quiet during operation. The other loco has 3 gears visible on the bottom of the truck, and is pretty noisy during operation. Can u explain the differences between the 2 locos? Also, which is the later version. Is one better than the other, and can I up grade to the latest model. Great looking loco, and it fits my switching layout nicely.