Took a short trip this weekend in my 2011 Mustang GT base. I have an SCT tune, on the way over I used the stock tune and got 19.3 miles per gallon.
on the way back I down loaded the Performance tune and got 24.2 miles per gallon.
The trip was approx 250 miles each way, on the way back I used the air conditioner most of the trip.
Has anyone else had these kind of numbers?

This is a reply I recieved:

(I assume the trip was mostly highway? I'd guess 19.3 was just calculated oddly by the car computer thought since that would be really low for highway driving. The tune does definitely increase mileage but in your case maybe there was a significant headwind on your trip there?

24-28mpg is common for highway mileage of the 5.0, and awesome for how much power is under the hood.

To be honest gas mileage has so many variables its hard to isolate causes of these things).

This is my response to his:

This is the second trip I've made in the last couple of months, same route. Trip is mostley on I-5. Used the same tune however, just reversed the tune. Performance tune on way over and stock tune on way back. Basicly same difference in mileage.
I'm going to get ahold of Bamma SCT and see what they think.

 

Elevation change between locations?