Mine has the LB7 engine, which came out in 06. They raised the power but hurt the milage. It's got 115,000 miles on it of which about 40,000 has been pulling our TT and another 20,000 pulling an equipment trailer. Even when I'm not pulling the trailer, its heavy and weighs about 8400 lbs full of tools and 100 gallons of fuel. I get around 18mpg on the hwy without the trailer and 9.5 to 11 pulling the TT depending on the wind. The equipment trailer weighing about the same weight as the TT but much less wind resistance gets about 12 loaded. I've kept track of every gallon its used since new and the overall is 14.1mpg. I don't know about around town seems like it runs around 15, however I've never checked it.
As a side, the computer mpg varies a lot from tank to tank and I don't trust it.