So I installed the Flowmaster outlaw axle back on my 2015 gt. Love the sound (except in 6th gear), but I have lost mpg, and in 6 th gear between 55-65 MPH the car will hardly go. So I'm thinking Ford racing stage 2.think it will help?

 

The gas mileage thing is probably more likely using the throttle more to listen to the exhaust. The exhaust shouldn't have adversely affected your 6th gear acceleration, I'm guessing its your imagination. Flowmasters never have sounded good cruising, too much droning.