Let me tell you our experience, then you decide. We had a 2005 Dodge Dakota (gas), pulled a small 25 foot 5th wheel. We got 17 mpg ave. while not towing, and 8-9 when towing. Bought a 2004 Dodge Ram, Quad cab, diesel, and tow a 34 foot 5th wheel. DH added the Banks system to our Ram. We get 19-23 mpg when NOT towing and 12.5 mpg when towing. Yes....the 5er was FULLY loaded -- we're full-timers and I refuse to "do without".
EACH year of the pickups has different torques, etc.....check them out fully. Each 5er/TT has different axle weight, etc.....check them out fully.