2003 Chevy Tahoe better mileage

air filters wont change much unless you redo the exhaust also. you can only take in as much as you can let out remember that, and the more air will mean more fuel. giving more power but not necessarly more gas mileage, or very little increase.

you can use a tuner for it but those arnt always cheap, and you can squeek out 3-4 mpg tops.

but rememeber your best bet is to go with a smaller engine or to adjust your driving habits.