At about 2,000 miles into the AEM intake test, we discovered why we were losing mileage. We were down to almost 13mpg cruising on the highway. One day on the way to the office, a horrible squealing started under the hood. The A/C compressor pulley/clutch assembly had died. We swapped in a pulley from a junkyard donor and were back in the mileage ballpark again. We were told repeatedly to swap the entire unit, that the fix wouldn't last, but over 5,000 miles later it is still going strong.