Can a 3 ton jack lift a box truck?

It depends on the weight of the box truck. If the weight of the box truck is within 3 tons (6,000 pounds), a 3 ton jack could potentially lift it. But most box trucks are heavier than this. Usually, they require a much higher capacity jack. 

3 Ton Floor Jacks

Trucks come in a wide range of tonnages. Commonly, you'll find light-duty trucks with a capacity of around 1 to 3 tons. Medium-duty trucks might have a tonnage ranging from 3 to 10 tons. Heavy-duty trucks can have capacities exceeding 10 tons, sometimes up to 40 tons or more.