I've tried searching this topic but no real direct answer. I have read on this forum and others that the 5.3 tune includes both an 87 and E-85 tune. To trigger the E-85 tune requires increasing the alcohol content to a point where the computer senses the change. There have also been comments that all of the E-92 ECMs will naturally advance timing if you continue to use 91+ octane fuel. Couple of questions: Is it true that the E-92 implementation for the 5.3 will function this way? If true is the horsepower gain similar to what people are seeing when they use a custom tune? Thanks in advance.