I put a Jet chip in my 2000TJ a couple of months after I bought it. I noticed no difference in power at all. It did cause rough idle, stalling, hard starts, and a 2-3 mpg decrease. I took it out and the engine runs fine now. I don't recommend it. I recently put on a performance exhaust...Huge power gain!!...spent less than the chip cost too.
JP mag put it on a dyno and LOST 1 ft/lb of torque and only gained 1 hp top end. Putting a colder thermostat in a fuel injected is not a good idea they need to be hotter than a carbed engine to produce power. Their are many cheaper hp mods than a chip. $260 for a 1 hp loss is not a good buy!
After installing a K&N filter and performance exhaust system I have a huge power gain. I tried the chip after the mods also and it made no difference other than the before mentioned problems I talked about in my last post.
Maybe my chip is defective, I don't know. Hopefully some others will post their experience with these.