Looking at a 3500 Dually. What kind of fuel mileage can I expect? Assume stock no chip. I know it as an exhaust system on it.

 

4x4 or 2x4? Automatic trans or manual? Regular cab or quad cab? Rear end gear ratio? All of these things make a difference! Impossible to answer your question without more info.

 

4x4, Auto Trans, Quad cab, No sure on rear end...Like I sad LOOKING..

 

if it has 3.73 gears, then around 15 to 16 city and around 18-20 hwy

if it has 3.42 gears it will get slightly better mpg, if it has 4.11 or deeper gears it will get substantially less. Driving it like grandma will help a little bit, but not much.

Obviously, when you are towing, mileage will decrease substantially, depending on amount towed and if you are driving up some hills.