Did exactly as it said it would
With having larger after market tires on the truck and checking my speed with my GPS, I was moving 4 MPH slower than my speedometer was reading. After a couple of programming attempts to dial in my tire size so my speedometer would match my GPS. I am very happy with the results. Now my truck runs a lot better, transmission shifts better, and PMG improved.
Does as Advertised
It calibrated my speedometer since I put larger tires on. It takes trial and error. Just because you put 35" tires on doesn't mean you just set this to 35". You have to test it. I have 34" tires. Had to set this thing to 32.5" for the speedo to be accurate. Unfortunately, this is my only option at this time since the tuners are unable to calibrate the 2015 F-150 at this time. Dealership wanted the same price as this calibrator for a one time change. Good product.