I have a 2011 Sierra crew an w/5.3 aluminum block. 3.42 rears. I am questioning the mileage my computer says I am getting. The computer is correct I guess I just wish the mileage was better than an average of 13.2 mpg with 87 octane. It's pretty hilly here in western Pennsylvania. I don't mash the pedal. I think I baby the truck. I swapped the stock muffler with a magnaflow SS, 14x9x5, 12229 model. I just swapped out air filter element with an AEM DRYFLOW. No real change in mpg. Got 220 miles on air filter. Truck has 4k on it. Will the MPG GO UP?