The only thing that might be wrong would be the "Distance Til Empty." I believe the fuel economy is based on how much gas is being burned, not by how full the tank is. It's probably something the dealer can change, most likely a simple "Has 34 gallon fuel tank" option.

 

I Wonder if maybe the electronics in the fuel pump or the float dont tell the ecu what size the tank is.

 

has anyone ever dropped their tank? is there maybe an electronic plug that goes to the float/sending unit? maybe the floats are different between the 2 tanks, hopefully if you plug in the larger tank, it will know by the sending unit that is connected? is that possible?

 

This is all I could find in the wiring diagram about it. It will usually show different configurations for optional equipment but it does not in this case. Just shows a variable resistor.

 

I've never looked at one, but I doubt the electronics are different. It makes more sense for them to program that stuff in the computer. Your needle should still be accurate since that's based on how high the float is. The overhead might also still be correct now that I think about it - and if it isn't, who really pays attention to the Distance Til Empty anyway? I've found it to be horribly inaccurate straight from the factory.

 

I just got off the phone with the Dodge Parts Dept. They told me that the sending unit in the tank is different (part #) for the 34 gallon tank. Hope that answers your question...