i've had one on for a couple of weeks now.
found on on craigslist for $250.
There's 5 main things it will let you do:
1. throttle adjustment (stock, gas saver, performance, extreme). since we're throttle-by-wire, it simply changes the "slope" of how the throttle responds when you press it. the more the agressive the setting, the more% of throttle is in the first 1/4 of you pressing it. instead of 1/4 way down = 25% & 1/2=50%, it becomes 1/8 = 25% & 1/4 = 50%, etc. or that's just my way of explaining it.
imo the stock, gas saver, sport and extreme only control the throttle sensitivity, not the hp gains. the selected octane (below) solely controls actual power increases. i've driven in all the modes and in gas saver if i do 100% throttle it feels the same as if i do 100% throttle in the other modes.
2. rev limiter. i see no reason that we'd need to change this. imo our -truck- engines do not use parts that are suitable for high revs
3. speed limiter. not sure that a pathy should be able to go over 109mph.
4. remove wot restriction. as i put in another post, i've found that if my coolant temp goes above like 195F, the engine goes into like 80% power mode, and the clutched fan is on 100%. same goes if you remove the wot restriction. could definitely feel it pull more off the line than before, when it's ~85F or less outside (so my coolant temp will stay around 190F without the clutched fan at 100%). as the weather cools down i might be able to comment more on this.
5. octane. this is where you get the performance increase. if you use 91+ octane then you'll get the "up to 35hp/torque" deal. i -definitely- felt an increase. after i upgraded to the bfg at's i suffered the big decrease in hp/tor. felt like i had a car full of adults and snowboard gear, when it was just me and empty. after i selected the 91+ (i had already filled up with it) and sent the new tune to the car (~5 min) i felt a significant improvement in get up and go. also feels like it pulls more in 3rd gear around the 3200+ rpm mark.
while on a completely stock pathy you'd probably get some mpg/power gains, i've seen negligible differences on mine. before i was getting 11-13mpg after my tire upgrades, and i'm still in that range.