Finally took the plunge, got a tuner, installed the 91 tune on my 08 GT auto today (otherwise dead stock expect for Boomtubes. Stock airbox-no CAI).

First impressions: throttle response is hugely improved. In fact you have to be careful or you'll lurch away like you've never driven a car before. I accidentally barked the tires just trying to reverse. If this were a winter driver I would be very cautious with the throttle. Since it's doing this on bone dry pavement I imagine it would be more than a handful on slick surfaces.

Shifts are noticeably firmer but not jarring. Trans is also holding onto the gears longer. Onto the highway, full throttle, chirped the tires on the 2-3 shift. That put a huge smile on my face. Full throttle laid a patch on the 1-2 shift. This car has NEVER done this before. Tried driving in second up to about 3500 and flooring it, threw me back in the seat quite a bit harder than without a tune.

Even the gas mileage seems comparable, or even improved, but need longer to know for sure.

Only thing I am not crazy about is that Brenspeed changes the parameters for the fan, so it's on almost all the time.

Bottom line; significant improvement over stock. Car feels punchier, more like a muscle car. Torque curve feels fatter. Even part throttle take-offs seem stronger.

Basically, as many others have said, the car now drives the way Ford should have done it from the factory. It's not quite a whole different car as some have claimed, but it's an amazing bang for the buck mod.