I had asked about it too, because it was used and never done before they advised me not to since tires won't match and have uneven wear! I agreed, and they said If I get new tires in the future they would. I had no issues with that answer.
if anything, its better for the longevity of your fuel system if no MPG increase! Don't fall for fuel cleaning system from Ford if you run high octane.
Looks great, I just did the 5100 series level lift 2.9' adjustable non sas, everything else stock and 35" tires. I love it and no issues. About 5" more lift with tires