Rough Country Speedometer Calibrator for 07-18 Chevy/GMC 1500/2500HD - 90009T

Install was a little more than what I expected not a simple OBD plug in. You have to plug this in behind the gauges and getting there you have to pull a lot of your dash apart. I left in the usb cable and ran it down near the OBD port plug in so if I needed an adjustment I did not have to remove this you will want to as well. I had my son download the software update on his computer and it was straight forward. You can adjust by tire size difference or speedo reading vs GPS mph if you have that info. I did from my radar detector showing that at 70 on my speedometer I was actually going 77. After I put everything back together my gauges did not turn on so I had to take everything back apart and plug in the harness better so make sure you push the harnesses together firmly the first time so you avoid that 2nd dash strip down. After trying I was amazed at how accurate it was at all speeds to the exact MPH. 33 is as on the GPS, 75 is 75 on the GPS ect. This also cured the MPG calculation offset as well as reset the factory shifting points as if you had stock tires. I had been getting some weird shifts in low speed situations when trying to drive slow though like parking lots and this device really smoothed that out. Overall this is a must have and well worth the money. Highly recommended