It shouldn’t be a problem if your rails are always the exact same distance apart. If they are closer than the red centering wheel it will get stuck. I usually have it about .05 stud smaller than the gap between the rails.
Is the MeshPart block under your train CanCollide true? If it is maybe it’s hitting the rails?
In Studio Settings go to the Physics tab. There is a setting called Show Contacts or Show Contact Points.
Click on that to show red balls that indicate where items are touching when you Run or Play test your train. That might help you with the problems you keep having.