I agree with everyone else. You'll most likely get it done much cheaper at a speed shop as well. I don't like to always rag the dealerships because mine in town is very good despite the fact that they told me a 3:73 gear install would be about $600 and they wouldn't even be able to compensate the speedo. Shop around. The more educated you are on what you want done the less you'll get screwed.
Good luck
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66 Tahoe Turquoise Coupe
Laser Red 96GT Ragtop
Both are slow but easy on the eyes!