I have a Jet chip I got from someone with a 5.9L 4wd Ram, and he said it made a big difference, did hurt mileage, but, made it shift firmer, run stronger, etc. But, when I put it on my truck, I noticed nothing...gas mileage was the same, etc. Than again, the truck I had was an SS/T and the computer was already different from the factory, so...that could've had something to do with it.
I think alot of people just want to justify their money spent. All the chips do is trick sensors, just like the "powerwire" tricking the IAT sensor. This isn't good, it just screws up the A/F ratio, doesn't help anything.