3DSMax costs several thousands dollars for a legitimate Copy, and seeing as you didn't mention paying that or yelling at a customer service rep at some point Im guessing you didn't pay that. That said, Blender is free to download and use, though not the easiest to learn, however it is the recommended to use 3D Creation program for Trainz atm. After that all I can do is echo the previous person's comment about Sketchup which is that its very poly heavy. To the point that anything more complicated then a Box is likely to drag on Framerates. I do have and use some sketchup models, but they're all buildings of not overly complicated designs......
Good Luck in your endeavors regardless,
-Falcus