Don't spend your money
I have a 99 Durango with a 5.9 liter engine so performance was never an issue, I was looking for the economy factor. There was no discernable difference in performance. I filled the tank @ 11.6 mpg prior to the installation, my next fillup was 12.1 mpg a statistical anomaly likely due to my observing my driving patterns. At that rate it will likely take longer than my vehicle will last to pay for the module.
I bought this PCM mainly for the mileage gains and it has helped somewhat. I don't have an exact figure for it but I have been able to squeeze more from my tank. This product really shines in the performance aspect. When driving normally, shift-shock is almost non-existent, and at full throttle, shifts are firmer and a power gain is very noticeable. The ride as a whole is much smoother, and has noticeably more torque across the RPM range. I highly recommend this product.
Not bad for the money
It hasn't been installed long enough to tell the mpg yet. I installed it with an afe intake. I figure I should see a difference in the gas mileage and I can feel a little power difference. I didn't have to push on the gas pedal as much to do normal driving. Overall I'm satisfied with the product.