Settings A/F on EFI

I am running a .030 over 383 with MSD, 484 cam, Performer Al heads, headers, 3.91 rearmed, 727 trans. My problem is with he EFI, I think. This sucker sucks up the gas. I can smell it running rich at idle and suspect it is doing he same while cruising. I suspect I am getting only 6 miles per gallon of premium non alcohol 93 octane. The A/F ratios are those that FAST EFI EZ says to start with. I want to increase the ratio at idle and at cruise. How much do I dare go. I would like to bracket the best set point. By that I mean I would like to set the a/f at the max and then drop back from there to find the best setting. Sneaking up on a setting may not give me the feel for what it is like at the max. Can anyone provide some advise? Thank you for any and all input.