I have a 2004 GMC z71 5.3. I had a guy put a tune to it and now I cant seem to get better than 11 mpg and thats on a good day. I have changed everthing that would consist of a tune up including cleaning my injecters. I brought my truck to him to tune for fuel econmy but lost major mpg sense then. I know he used efIlive so thought maybe someone may know something he dont? Please help !