Driving home from Hilton Head SC to Rome, GA I got 24.9 mpg going between 60-80 mph with the wife, son, weekend's luggage and AC blowing.

Seriously, what is not to like about this car?

It's a Mustang and you probably passed 300 on your trip.

Haha, was about to come in and say something similar, touche!

My 06 Mustang GT got 29 MPG on the highway if i cruised steady at 65mph. Normal would be about 24mpg. Love the boss 302

Haha, was about to come in and say something similar, touche!
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I'm hard pressed to think of anything that would concern me less. If anything, the Mustang's ubiquity is a plus, as that's the reason it has such tremendous aftermarket support.

Great car indeed, but that's less than a Corvette would get in a similar situation. I'd call the highway cruising mileage just "ok". That probably wasn't a primary reason for getting the car though

No doubt. The Corvette is unquestionably the better car, but I needed a back seat. Still is there a 4 seat, V8 car that gets better mpg?

that is better than my 2013 M3. It got 22mpg at 80mph on a recent 2 hour trip. Is the Mustang's 6th gear an overdrive gear like the corvette and viper or is it useable to accelerate?

According to fueleconomy.gov 4.0L Audis and 4.7L Mercedes are slightly more efficient (26-27) and BMW 4.4L and HEMI 5.7L are about on par (24-25) with the V8 mustangs. Not sure about real world for those cars though. I don't know if the Mustang is a stand out offering but it certainly shows how much progress has been made in terms of Fuel Economy.

With cars like that it's all about how tall 6th gear is. Hell, a modern Dodge Ram or Chevy Silverado can get 24 mpg hwy, and that's a 5500lb truck