Q&A: How can I improve my mileage on my 2004 V6 Mustang convertible with 67000 miles on it?

I know you say you service it regularly, but once again check the air pressure weekly. Emissions modifications often come with no noticeable difference in gas mileage unless your vehicle tuned to take advantage of them this way. Often times when I use Seafoam on my car, I get better gas mileage. There is copious information on doing this. Also with experience in owning several vehicles that were RWD/AWD, you can change the differential fluid with synthetic (ALWAYS make sure you put in the correct amount) and you may notice a difference in mileage. My RAV4 (AWD) often gets 2-3 mpg better when I change the gear oil in the transfer case and rear diff. However, as the poster above me stated, LAY OFF THE PEDAL. Make steady and slow starts. You can also use the natural braking power of your engine when you need to make slight adjustments to your speed — such as following traffic at lower speeds — to get better mileage. If you drive a stick, learn to heel-to-toe downshift and you will seriously benefit from using your engine to brake versus clutching and brake pedal. You will also learn a very valuable skill.