Can anyone tell me (or point me to) where I can find out the differences between the LGA1 and LGA2 computer codes on a 5.4L Supercrew? Why would there be different computer codes in the first place on an identically configured vehicle of the same model year?

My buddy and I have the exact same truck only different colors. My code is LGA1 and his LGA2. We're trying to figure out why there is such a big MPG difference between our vehicles. I'm perplexed...