I don't have a chip but am considering the Quadzilla XZT. You can view a lot of comments at:
http://www.dieseltruckresource.com/dev/index.php
http://www.turbodieselregister.com/
Most chips probably won't help mileage because they increase fueling, one way or another, to reach their goal of more power. The XZT, Edge Juice, and TST possibly (uses a lot of timing),
may be exceptions, if used judiciously. If you add a chip you become your own warranty station though.
XZT about $350-400
Juice and TST about $700-800
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