Installation is free - you're going to do it yourself, right? I removed mine when it malfunctioned to re-route heat to the cab in winter.....simple to do.

Not sure on price of a new one, though.

As for MPG, I'd say 25-28.

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79 300SD - $50 out of pocket purchase
03 Dodge Ram 3500 CTD
2003 VW Jetta TDI