My rig build and upgrade thread is in my signature. I get about 18-22 without the camper and 16-18 with. I'm quite satisfied with my junk's abilities, handling, etc.
I should add: my camper rig is the 3.4 V6. My wife has the identical truck but the 2.7 I4, and I would not put my camper on her truck. There are some guys here that have done it, but I can't imagine how anemic that would be so cant speak to that configuration.