In all the stuff I wrote, I didn't get into all the variables. Like, what is your tire pressure? Factory tire pressure specs are great for a nice ride, but horrible for gas mileage and tread life. I run my Z-71's tires at 45 psi. I feel the seams in the road, but get better mileage from both gas and rubber. Can you make yourself drive and NEVER open the throttle more than about 20%? Can you stick with or under speed limits? Do you drive over 55 mph on your highway drives? Do you ever pass slower vehicles? How long do you have to wait at stop lights on your city drive? Do you coast long distances to places you know you will have to stop? Or do you pull the speed down quickly at the last second using the brakes? Is your route flat and straight? Or is it hilly with curves? Are you running with the climate control set to "Auto" (which runs the A/C compressor)? Are you running with the windows down? Have you added any goodies that increased the truck's weight or it's wind resistance? All these things factor into it. Do you buy only "top tier" gas? Or do you fill up wherever it's cheapest? Some people think "gas is gas," but that is not true. Off-brand gas causes carbon and crud buildup in the intake and combustion chambers. Are you running pure gasoline? Or are you buying E10 because it's cheaper per gallon, or because the state forces it on you? E10 ethanol-blend lowers gas mileage by 8% on every computer-controlled vehicle. That's almost 2 mpg off of 21 estimated. Here in Iowa, E10 costs 10 cents per gallon less than regular gas. As of today, that's a 3.2 % lower price. But with an 8% drop in mpg, that means the "cheaper" E10 actually costs about 5% MORE to use. "Fuel economy" is NOT "miles per gallon." It's "cents per mile." The EPA tests, even revised for "real world," are still done under perfect and controlled conditions. The manufacturers increase the tire pressure. The test is done indoors in fixed temperatures. The driver treats the gas pedal like there's an egg between it and his foot. I betcha, if you were to... Inflate your tires to 45 psi... Run two cans of Berryman's or Techron through a tank of gas... Buy only Phillips or BP or some other top tier gas brand for about 3 tanks... THEN do a gas mileage test, if you can stand it: Pick a dry day in the 60's with no wind. Fill the tank at a particular top-tier station, using a particular pump, on the slowest setting. Stop when the lever kicks off. Drive at least 100 miles. Drive strictly 55 mph on straight, flat interstate. Push the "snowflake" button on the climate control, to turn off the A/C compressor. Windows up. NEVER push the gas pedal more than about 20% open, and press it softly (like there's an egg between it and your foot). Coast to slow down. Use the brakes as little as you possibly can. Refill the tank at the same station, using the same pump, on the same setting. Stop when the lever kicks off. ...your Tahoe would get about 24 mpg.