I have a new 09 Silverado 1500 crew cab with the 5.3 flex fuel active fuel management engine. I wanted to check highway gas mileage as accurately as possible. I went to a specific gas station, picked the most level pump and filled up with 87 octane on the slowest feed setting until it automatically kicked off. I drove 140 highway miles round trip using cruise control set on 60 mph. I filled up again at the "same station, same pump and same slow feed until it automatically kicked off." Results 23.7 mpg . . . . I was thrilled with the results. I followed the same procedure again a week later for a round trip of 188 miles (this time part of the trip included a tour through an RV campground with some very steep hills . . . . therefore I knew my gas mileage would not be as good. Results 22.0 mpg . . . . again, very happy . . . . . . . . MY QUESTION: I NEVER SEE AN INDICATION DISPLAYED DIGITALLY THAT THE ENGINE HAS SWITHCHED TO 4 CYLINDERS . . . . WHY???