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Visibly: The GT has bigger wheels, it has fog lights, usually a spoiler, dual exhaust, and sometimes a fake hood scoop.

Mechanically (where it matters):, there are more differences. The GT has the V8, a better transmission (if manual), bigger brakes, a stronger rear axle, a stiffer suspension, better tires, and sometimes (depending on the year), a shorter rear end gear.

Generally, the 6 has the mustang stripe/decal along the bottom sides. Most 8s have large foglights on the grill. I say most as there are kits to make 6s look like 8s. Interior and chassis wise, there's almost no difference.

I recommend you get the newer 2011 mustangs because the 2005-2010 mustangs are so f ing slow compared to the competition and the 2011 mustangs.