I have a Flashpaq on my 2009 JKUR, it has 84,000 miles and has never had a problem related to the programmer. I had it installed along with my other engine modifications (CAI & throttle body spacer) before I picked it up after purchasing it, so I don't know how much of a difference it made because I never drove it stock. It is significantly slower than my '07 4runner (or at least feels that way), but the 35" tires probably don't help. It gets up to 80+ mph pretty easily though, so I assume it has helped some. Just make sure it doesn't get unplugged during the install because that will give you some serious problems. As far as gas mileage goes, I average 15.8mpg for DD and 17-19mpg on the highway (speed dependent), which isn't too bad for a 2.5 inch lift and 35" KM2 tires. Hope this helps.