07 Tahoe with AFM

I havent tuned any gas vehicles before and i have a customer that has a 07 tahoe with AFM and they were wondering what the raise in mpg could be? I pulled the stock tune off and looked at the AFM settings and it looks like GM put it on there to ask more for the vehicle and have it barely work. If anyone is kind enought to share some of the settings that they have tried and been successful on and got a increase in mpg at cruising speeds that would be great or any other pointers that someone can give me to help raise the mpg in a gas. Im use to the duramax's.
Thanks