your doing better than our son's work F250 gasser. He pulls a 28 ft Vnose that weighs about 7500 lbs. Best he ever gets is 9, more often barely 8, sometimes as low as 6.
And it isn't that he is going fast, working for the state one thing one NEVER does is go over the speed limit and they actually pretty much require him to follow the truck limit, even though legally he doesn't have to. So..... he's seldom over 60, and most of the time he is on rodes with a 55 limit.
His previous truck was a Dodge with the 5.7 hemi. Mileage wasn't noticeably different with the Dodge.