An auto car on a tow dolly?

Not sure of what types of grade you are talking about but you said pass? Another drawback to the tow dolly is the lack of tongue weight and lack of brakes can put the tow vehicle into slide easier than if it was carrying some tongue weight and a means to slow down the 3k behind you. A downgrade, 3k pushing a lighter truck, and the tail is going to start wagging the dog. Without trailer brakes there's no way to calm sway.