1999 Blazer Chip?

I am looking for a gas mileage increase. Have any of you guys put a performance chip in your blazers? If so did it help out your fuel mileage any? I just got my blazer last and have found out it's not that great as far as gas mileage. My mom had a 93 model S10 ss with the same 4.3. It's mileage wasn't outstanding but it beat my blazer hands down. My blazer is an LS with diffrent shift points so I figure that has a lot to do with it.