That's interesting. I think roger_04_rt is probably correct in thinking that there's something else at play in this case. The Power Controller and Juice can only modify fuel during open loop operation (accel/decel... changing throttle settings). Fuel mixtures during cruise (closed loop) are driven by the O2 sensor. Therefore any significant changes in mileage are going to be driven by something other than open loop input.
Sorry it didn't work out and I wish we could have figured out what was behind your change in MPG.