Ford F350 7.3 Gas Pulling 15k

I have one of the new 7.3 fuel mileage combined city and highway is right about 14.4, I have not towed my camper yet with it because I’m still within 1000 miles break in, about 3500 RPM the truck sounds like it has a Flowmaster on it, it’s not annoying but you can hear it inside the truck