I got the JET chip from a friend for $50.00. It is definitely worth that. I felt performance gains throughout the rpm range. My acceleration after installing the chip and 32" tires was better than stock with 30" tires. I now run higher octane fuel which costs a bit more, but as long as I keep my right foot off of the floor board, I seem to get about 1.5 mpg bettergas mileage with the chip. Just today I removed the stock airbox and put on a cylinder racing air filter. Holy shiite!! With that and the chip it must have at least 30 more horsepower.
I really don't know if I'm damaging my engine. I doubt it if it's running this good! Time will tell I guess. I'm keeping a close eye on my plugs and O2 sensor for any signs of weird mixture or heat or anything.
'99 TJ Sport, Coil Spacers, 32' AT's
JET Chip, custom Air Tube/Racing Filter,
Bent fender, Upgraded Brake rotors/pads.