Alot of people believe that a programmer, intake and exhaust are all you can do to optimize fuel economy. Just the tip of the ice berg. The LLY has huge potential, in our eyes it gets the best miliage of all years. I just got back from a 3,000 mile trip with my 05 crew cab dually with 285-75-16's AT's(you know the tires everyone says hurts your milieage) I pulled a tall horse trailer bumper pull, weighs 6500 lbs. for 1500 miles Drove 80mph the entire way, averaged 12.5 mpg. Turned around empty drove 80 to 85mph back home, averaged 22.9mpg calculated not relying on the dash. Speedo is corrected for tire size. Gains come from small things all adding up. Stay with programmers, stay away from tuners like Banks and Edge if you want miliage. Get rid of cats and egr systems that flood the motor with garbage air, open up the intake elbow by the turbo, seal up the radiator and intercooler to force the air through, electric fans are the tits! Water/meth injection will keep the miliage up while towing and egts down. Remember black smoke maybe cool, but it won't make power.