I just bought a 2015 Buick Enclave last month. I started tracking the fuel economy by using the gas pump reading and the odometer as well as the cars monitoring system. I am getting less then 11 MPG around town. I take it easy on accelerations and coasting to a stop. It looks like others are getting better millage. I'm concerned that there is some other problem that isn't throwing a code yet. I changed the air filter to see it that makes a difference?
Welcome. Air filter doesn't normally impact mpg on a fuel injected engine. Going by the road tests I can find on the Enclave your fuel consumption isn't that below par. When you say "around town", how long a journey are you talking about? Do you spend a lot of times sitting at red lights? If you are stopped at "long" lights, do you switch the engine off? Driving style has a big effect on mpg. For best figures you want to accelerate briskly and avoid using the brakes. This requires good anticipation. Choose your route well and if you have a regular commute then learn it well. I know exactly when to take my foot of the throttle, wet weather or dry (very different), on my regular routes.
After a longish trip, try stopping without heavy braking (ideally no braking). Immediately check the temperature of the wheel centres (be careful not to burn your hand). If a wheel centre is warm you could have a brake rubbing, which will need tending to.
Please do not fall for these misconceptions. Your vehicle's gas mileage will not be affected by an air filter, your lawnmower however will.
How long of trips are you going on? When I had my 2005 4 cylinder Honda accord I would mostly drive it to school, a 3.3 mile trip. I usually got 23 MPG going there and 30+ coming back. I was hypermiling and had performed fuel economy mods to the car, and I still just matched the EPA city rating for that car in those short trips. Short trips are terrible for fuel economy.
You aren't idling your car to "warm it up" are you?
I'm talking about a mixture of 35- 45 mph surface streets some stop lights. Doing the same kind of driving in our 2003 mini-van with three rows of seats we get about 17. The tire pressure is at spec.
Going above spec won't hurt. Are the tires new? The rolling resistance is worse with new ones. Does the car have AWD? can it be turned off?
In addition to brake drag, bad alignment can reduce fuel economy. Won't hurt to use fuel system cleaner.
What was the minivan? Did you calculate its fuel economy, or just go by the display? Are you driving the SUV the same way as it, or trying to be more efficient? It sounds counter intuitive, but automatic transmission cars tend to get better fuel efficiency with being a little aggressive in acceleration until you get up to speed. Slow acceleration could mean staying too long at less efficient gears and out of torque converter lock up.