get a better car
Depends on the fuel mileage of the vehicle you are driving and the price of fuel along the way.
Probably the best way to get better fuel mileage would be to get a tuner for it.
They are about the same in fuel mileage but the 6.0 is thirsty.
There is no fuel additive that will increase mileage. This is a myth. None of the snake oil additives work.
Better mileage
The best way to get better mpg's is with a tuner/programmer. Most out there guarantee better fuel mileage.
diesel.
10 bolt or 12 bolt has NOTHING to do with gas mileage. It is the gear ratio that is inside of the rear end housing that affects the mileage. The lower the gear the lower the fuel mileage is. The higher the gear, better the fuel mileage is.
less wind resistance, better fuel mileage
Less weight = better fuel mileage.
Better fuel mileage and cleaner emissions.
take one foot off the accelerator