I have only ran one tank full and due to the battery being disconnected to fix the seat the mileage is to the best of my memory, but I got 18 1/22 to 19 mpg which for a truck its size aint bad. But what would give the most improvement in MPG? K&N or other cold sir system? Tonneau cover? Chip?

 

If looking for MPG increase, go with a 100% synthetic lubricant in everything you can put it in. Engine, tranny, P/S, wheel bearing and so on. I use AMSOIL in everything that I use. It's also cheap insurance for your components. As far as a different air system, if you're looking for MPG and not too worried about a decrease in HP, then go with a warm air intake. Since warm air has less O2, the computer will inject less fuel thus saving on gas. A cold air intake only increases fuel useage as colder air has more O2 thus the computer will inject more fuel. As long as O2 sensors are used in vehicles, the computer will always try to maintain a 14.7:1 air/fuel ratio. On my 04 Freestar with the 4.2L. I run a water injection system from AQUATUNEwith a 75/25 mix of distilled water and 99% Isopropyl Aclohol, Autolite copper core plugs gapped at .048 and run a larger snow tire (HANKOOK HPW401 P225/75R16 with 42psi in the fronts and 40psi in the rears as I pattern my tires) all year long. This past christmas visiting our Son (Dayton, OH) and Daughter (Wilmington, NC) the wife and I averaged 22.3 MPG (This is actual figures, not the Freestars computer) round trip from Yorkshire, NY to Dayton, OH to Wilmington, NC to Dayton, OH then home to Yorkshire, NY. Ran 80-85mph most of thetime with A/C on and loaded to the gills with stuff. I average 27mpg to Buffalo, NY (actually a downhill run even though the terrain doesn't look like it with all the hills) and 24-25mpg on the return trip. The wife DOES NOT get good mileage due to driving habits. Same trip to Buffalo and back, she's lucky to get 17-18mpg.I use AMSOIL 0W30 Series 2000 in the engine and their ATF in the tranny and P/S unit. At this time, I'm still playing with ideas and pieces on the Freestar to get a constant 30+mpg.