Performance chips... are they worth the money?
 

I recently lifted my jeep and gave it a new set of 31's. A friend told me to buy a chip to fix the mileage change and the shift points. He also mentioned a small boost in HP...
Do these chips really work and if so which one should I invest in?

They're not worth an ounce of time on 31's. Save your money for a rainy day.

What you're looking for is not a "chip". It's a calibration tool. You will need one to recalibrate the speedometer, if you had the 16" wheels with 29" tires then your speedo is going to be off by about 7% which is meaningful... you will be reading 70 mph and actually traveling at 75mph for example.

I don't do automatic so can't comment on shift points. There's no performance improvement to be had.

There are some "tuners" that claim to improve performance or mpg or both. I think it's unlikely they make a meaningful difference. There's nothing out there short of adding forced induction or switching to something like megasquirt that will make meaningful horsepower differences, and with 31" tires, you likely don't need any performance improvement. hundreds of thousands of JKs are rolling around on 32" factory tires with no problems.