hauled off some scrap metal yesterday. weighed in at a little over 8100 lbs total each time. got on the 4 lane highway and stayed around 50-55 mph. filled the truck up before i left and when i got back after the 2nd load. went 109 miles on 5.130 gallons of diesel. averaged out at 21.24 mpg. i was shocked!!! this is with 4:10s and 305/70/16s. just thought i would share! 
but it wil get a hair over 20 mpg in double over at 62 mph 

. The reason is b/c i was estimating my MPG by looking at the fuel gauge and guessing how many gallons i used to go "x" amount of miles.