I purchased toyota tundra on 6 nov 2015. since owning the vehicle i have been getting 460 miles to a full tank of gas (38 gallon tank). those numbers equate to 12mpg in fuel economy estimates. i picked the vehicle up on 6 nov2015. the truck had a full tank of gas. the fuel efficiency read 570 mile for a full tank of gas. on 13 nov i drove the vehicle to florida. every time i filed up the truck with fuel the fuel efficiency reading started to decline. on the first three full tank of gas, the reading was 540 and 520 miles for a full tank of gas on 15 november. i took the vehicle to the dealership on or about 17 nov. the service department plugged the vehicle up to a computer. the computer sent out a report that showed that the vehicle was getting 18 mpg. the service personnel told me that i would be doing well if i got 14mpg. based on their comments i was not to expect anything over 15mpg over the highway. on 25 nov, i drove the vehicle to florida. i decided to manually track the mileage in regard to a full tank of gas with the use of the trip counter. i took pictures of the vehicle only registering 12mpg on a full tank of gas. on a full 38 gallon tank, i was only able to drive 460 miles per tank. that equate to 12mpg. the driving condition was 74-78 degrees; driving on i95; there was only three passengers in the vehicle. i used 89 octane graded gas.