Bryan I have an '05 Vision with the AC 355/380 and 3.90 rears. My last IFTA showed 8.01 mpg over the three month period ending in Dec. The previous showed 7.67 mpg and my worst one last year was the 2nd quarter with 7.27 mpg. All those are 3 month averages. I generally have my cruise set on 59 miles an hour or 1400 on the Tach. When the sensor on my EGR was going bad my mileage dropped into the ranges you are getting with your truck. Mine wasn't throwing any codes only the faint smell of exhaust was noticeable and even then everyone thought I was nuts when I said I could smell it. There was a recall on the exhaust manifold bolts that it seems hadn't been addressed. Those two things alone dropped my mileage down into the mid 5's to low 6's. I was in Phoenix at the time heading back to Memphis. I stopped in at Vanguard and had it checked and after two days of haggling and insisting they finally identified those two issues as being genuine. After replacing the sensor and changing out the manifold bolts my mileage immediately went back to my normal mid to high 7's. So it is possible to get good mileage from these trucks. Anyway just my two cents worth and I highly recommend that you check the recall on those bolts if you haven't already done so as they are what lead to my sensor going out to start with. Best of luck to you!
