*UPDATE*Calling Duramax owners 1st trip with camper bad fuel mileage

I have an 06 LBZ 3500 DRW. It is lightly tuned, and pulling my Fuzion fiver I get 9.5 to 10.5 at about 70 mph. I have not weighed this trailer, but my last Fuzion combined was around 25K same tow vehicle. It could be poor fuel quality. I would think if you had a major malfunction it would throw a code. That seems though that is really poor mileage for that type of load. I would have it looked at by the dealer to see if something comes up. It is a good motor, likely one of the best put in a pickup.