I've seen this on another site and was curious what LB7 owners here are getting for fuel economy. When you post, please post your cab configuration, transmission type, and if you have 2WD or 4WD.
Mine;
RC/LB, Auto, 4WD.
Average; 18.1mpg
Highest; 22.9mpg
Lowest; 13.4mpg
I know the newer trucks only come with the Allison, but I'm pretty sure you could get a six speed manual up until 2008.
If you crawl under the truck and look, it will say 'Allison' on the transmission pan, thats the surest way to tell.