my 06 ccsb lbz gets 12 mpg pulling 7000# trailer through the foothills of northern maine. the milage just dropped about a mpg from going to 265 tires from 245's.the 01xcab with 265's same trailer maybe a little more like 12.5 to 13. every tank on both trucks is hand calced and look at the dic on the 06.no comparison in power the 06 hauls-ss.