I have a 2007 GMC 1500 5.3 V8. Once I got 45,000

MPG is never constant, it is ever changing.

a good emitions guy could pin point a bad o2 sensor but replacing the front two is a good start.

1997 Mercury Villager FWD Van Fuel Economy Fuel Type Regular MPG (city) 16 MPG (highway) 21 MPG (combined) 18 Fuel Economics Cost to Drive 25 Miles $3.39 Fuel to Drive 25 Miles 1.39 gal Annual Fuel Cost $2152

change fuel filter. but if it does not work u might have some leaky injectors

The better the engine breaths the better the mileage. Was the new computer a stock computer or performance?

I have the same issue of low gas mileage. My 2008 Kia Rondo with V6 (2.7Lt) gets 20-21 mpg in average. Even for highway mileage, it is around 21-22mpg. Very poor gas mileage. Disappointed. I hope it would improve in the future.

Wide tires make less gas millage, get narrow wheels, let the car accomplish speed slowly from 0 to 30, look at air filter,if shortly replaced, oxygen censor, 15 miles is normal 16 miles per gallon is good for a V8

Not sure where you live but if the gas you get has a higher amount of ethanol in it you will get worse gas milage.But there are many reasons that effect gas millage.

If you have the RT with the 5.7 hemi as stated I do not beleive you ever got 27 to 29 miles to the gallon. the best that car will do is 24 - 25 miles to the gallon and that is on a pefectly flat and straight road at about 60 miles an hour. As fas as the MDS the best way to tell (if you can't feel it change) is to use a tool such as the dashawk that monitors the engine stats. I disabled the MDS for several reasons and really so little to no change in gas milage. I do not beleive the MDS helps as much as people would like to think. I have added a lot of mods to my hemi, but still think that 14 - 18 mpg under normal driveing is good for this car