Just for grins, what engine/rear end combo are you running? And did you opt for the Tonneau?

 

shes got the 5.3 non E85 motor with 3.73 in the rear with 17" wheels. no tonneau

 

Hm, we have the same motor/gear ratio except I have the Std Box, I average 16-16.5 city/highway driving (highway here is an average of 40 mph since I only am on it during rush hour, stop and go) and I have a lead foot 50% of the time, I could probably get 17-18 if I didnt drive like an idiot. I noticed after I hit 10k miles I got a *little* better mileage, nothing to write home about. Although on a 250-300 mile trip I averaged about 75mph with cruise on 95% of the way and got 22.5. So maybe its just a weight deal? The reason I asked about the tonneau was because on my last truck I got 1-2mpg better WITHOUT it on...