MPG increase with Performance chip

Hello

I have an 2000 4runner and have been looking at aftermarket chips to increase fuel milage. These chips do not replace the stock chip but work with the factory chip. I have one on my motorcycle and it works great. There are a lot of them out there and very widley in price. Has anyone used one of these. Fuel Maxx is one for example.

Thanks for any imput

See if this site has relevant information. I know he used a chip.

http://www.gadgetonline.com/4Run.htm