I was not impressed at all with the 91 tune on mine. Got worse gas mileage and performance was negligible. I did some long term testing for all tuning levels and am back at the stock tune modified for tire size & TPMS delete. This is going to vary greatly by engine though.... I think mine is a case of the 5.7L factory tuned for 89octane and therefore don't notice a big gain going to 91 tuning, and the 87 performance tune just didn't feel right for the engine. The only thing the tunes did help with was some throttle delay.... but its not enough to bother me in this vehicle, I'm not gunning it at lights and the 5.7 has enough power to get me moving when pulling into traffic even with a bit of torque management (throttle delay).
I also wonder if some of the mpg gains people are noticing are due to tire size adjustments. Some may not be accounting for the mileage difference of having larger tires than the speedo is calibrated for so their mpg reading is low until corrected. And others may be putting 32" for their tire size when the effective tire diameter is actually 30.5"- so their computer thinks they're driving further than they actually are which shows better mpg than actual.
Not saying that's the case for everyone.... but just food for thought.
Edit: Not discouraging people from tuners here. I recommend them for the obvious benefits for correcting tire size so the speedometer is accurate and the trans shifts correctly (which btw probably does help a bit with mpg.... but not +3). And any performance gains you get are an added benefit IMO.
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