lean codes on both banks

[bobmare]

merry x-mas to all.after letting my car sit a few weeks,I went to do some errands on sunday and while turning into a parking lot my car,07 Shelby gt,13250 mi.auto.,died.like turning off a light.went to my mom's on x-mas eve and it happened twice more,once when I turned off the freeway after a 50 mile drive on cruise running great and again when leaving, half a mile from her house.I hooked up code reader and got po171 and po174,both banks lean.I see others have had the same problem lately.could it be the ethanol in the gas.need all the help I can get.also,had it dyno tuned a few years ago and it has run perfectly until this.