The NV brochure shows the high roof 2500 SV V8 curb weight as 6139 and the high roof 3500 SV V8 as 6143.From that small weight difference it would seem both units are using very similiar componets if not the same components. The difference in weight I think can be explained by the tire difference. The 2500 cargo van uses a 70 series tire while the 3500 cargo van uses a LT245 75R17. This tire difference would also explain the GVWR difference of 9100 for the 2500 and 9900 for the 3500. There should be more equipment differences than just a tire difference between the 2500 and the 3500 since there is a significant difference in base price between the two vans. It may be that the Nissan marketing guys just figure since it is badged a 3500 series van they can automatically raise the price above a 2500 series and the customer will accept it even though it appears the tires are the only difference between a 2500 and a 3500 cargo van.