I have seen many adds for power chips that increase your mileage (getting 22mpg).
Has anybody used one of these? where do you install them if I do?

 

I haven't looked at one for my Sprinter, but I did have an Upsolute chip put on my diesel Beetle (I see Upsolute makes them for Sprinters as well). In that case it was a replacement chip on the ECU. It made a very noticable difference, especially at lower RPMs, while getting the same or better milage. Doesn't seem to have affected engine longevity, it's about to turn 300k miles, being chipped for the past 250k.

 

Be extremely cautious of chips for sprinters. For now there are only 2 credible companies doing actual ECU mods to sprinters. Renntech and Custom Spooling. There is no such thing as a generic chip - box or 1 map fits all for sprinters. Each unit needs its own unique tune, and you need to be specific on your needs and actual uses. There are 24 versions of just the 2007 642 engine, so 1 map will not do all of them. MPG increases are very good, speed limiters need actual modification to the ECU, no map will do it alone. Make sure you get a guarantee if your ECU has to be shipped to be bench flashed , simple static electricity has been known to damage the MB ECU and bench flash problems. It would be bad to make a paper weight out of it. I have seen pictures of dash screen shots of 30.1 mpg on a 2008.