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

Earlier you said that you "know your truck" or something like that, but back in the first post you said it was your "first trip."

So which is it? Is the truck new to you, or not?

If you've had the truck for a while, you certainly have an idea of the fuel economy it gets unloaded. How does the truck do unloaded? Was there a sudden drop in fuel economy unloaded?

A drop in fuel economy towing should also reflect in a drop in fuel economy unloaded. Maybe not as drastic, but you should have noticed it if you "know your truck" as you say.