how many mpg should i be getting on my 09 v8 4.6 3valve?

 

That is a very broad question. How fast/slow do you drive how much do you tow/carry is it hilly in your area, cold, hot, windy,high or low air pressure in your tires, type of tires. You could have five different people drive your truck and everyone of them would get different mileage. Even fuel blends in your area can affect fuel economy. If you drive a truck of any make you can't get real concerned with fuel economy. They are all about as aerodynamic as a refrigerator and heavy as a tank. Take a look at the factory fuel economy rating for your truck and plan on it being a mile or two less if you drive empty and are not towing. The more weight and higher speed the worse it gets for the majority of vehicles. Not the answer you want I know but it's the truth.

 

http://www.fueleconomy.gov/

 

Anywhere from 12 to 22 mpg.