Poor gas mileage
 

Hey, I have a 03 GM has 84000 miles. I can't get better then 19mpg, I drive 95% highway. I got the the car back in February from my father-in-law. He always bragged about how he would get 25-27mpg when he would come to visit. I changed the fuel filter, air filter, plugs, had BG fuel service done, cleaned the MAF sensor. Had the dealer run a diagnostic that came back good on all tests. I'm stumped any ideas what else it might be? Any help would be appreciated, thanks.

air pressure, rear gear oil, repack wheel bearings on front of car, do you have extra weight in the car that isnt needed?

One thing you might want to think about is your driving styles, he might have been easy on the gas. I know with my 97 GM. I am as light as I can be on the gas, and always look at the traffic light head and as soon as I see it change to yellow I let off the gas and coast all the way to the red.