Here's what I have noticed. Each boards mileage claims vary as much (or more) than the mileage I actually get with my own truck. My normal everyday driving I get lousy mileage. Although, I take a lot of short trips and even my longer ones as on So. Florida parking lots (highways). The heat and being at or under sea level doesn't help either. (Doesn't make sense to me, but I get MUCH better fuel economy once I hit the rolling hills of GA and it stays that way until I get back home from Connecticut or in last years case Tennessee)

Obviously the LMM gets worse mileage than its predecessors, and from what I have expereinced and read it has a lot more power, and a restrictive exhaust too. The best case people seem to say about 1 mpg less and others up to 5-6 mpg less. My LMM gets better MPG than my gas 2007 6.0 Suburban (4x4) and 2005 Denali XL (AWD) and about the same as my 2005 Ford F250, 6.0 DIESEL, 4x4, CC, SB. Which is around 12 in local driving in town and 14-15 on highwy drives, but I drive fast 75-80. And yes, I wish I got better MPG's, but don't we all?