Super Six fuel mileage

The fastest i drive this car on the hwy is 50. i was running 195-70-14's when i got the improvment of fuel mileage which is when i got the 30 i was also letting the car practically pull itself. I unfortunatly had to get rid of those tires since they were dry rotted. i have 215-75-14's on the back now and the car hates it. I forget what they call this new "green" style of driving, but you put the car in N when slowing for a stop sign or light. You also begin decelleration a much longer distance back having to use your brakes sparringly : ) (makes them last longer too). I like to practice these little methods being that gas is so high and the car is quite old. i try to do everything i can to improve fuel mileage. Now if these practices would just work with my 1/2 ton.... the thirsty turd