I recently bought this unit from a member here (Alex: Sierraowner5.3, who by the way is a great seller if you need anything he has!) for the 04-07 trucks (for obvious reasons ). As noted in my signature, my truck has an upgraded cam shaft as well as a few other engine mods, and when I had them done at a local tuning shop, I assumed that they had also installed a custom tune because they were using a computer and a dyno to track the power. However, I called the shop and they told me they were only doing that to make some adjustments, and said that a tuner would work great! The unit itself is extremely easy to use with simple yes and no questions. I noticed very little in the way of extra power at first since I didn't adjust shift points or anything, but once I did that it really seemed to have a bit more gimme. Not sure on actual numbers (yet, though I am hoping to use said shops dyno again to compare with originals that they still have logged, supposedly), but I did notice an increase in my MPG (1.36 average in 3 tanks to be exact) which wasn't mind blowing, but still acceptable. The main reason I bought the unit was to calibrate my speedometer for larger tires since my dealer said they would not do it, and I couldn't find anybody else willing to do it without leaving the place with all my limbs. With that said, that is my only complaint. I calibrated the speedo to the exact diameter of my tires, and it actually made my speedo worse! I had it set for 32.75 tires, and had to set it for 31.75 for it to be correct according to both my GPS and a local speed trap. I would highly recommend the unit. I could give more info about it if needed, but you can get all you need from here. Thanks again to Alex for selling the unit to me! Well worth the money!