I just recently did the SC 91 tune for my truck. I get increased mileage by 2 - 3 mpg over the 87 tune. But in reality I get decreased because I love the Snap and Growl that 91 tune gives this truck, Specially when Im little heavy on the throttle. Also my kids love the takeoff this thing has.

Don't think I could ever go lower than 91 again.