Why did you replace it? I've never seen one go bad.. Also If you order a new one from ford they can set the mileage to your pcm. Also your pcm contains the actual mileage that the car has. So no matter what, if you plug a diagnostic tool into your car the mileage that is in the pcm is the correct mileage for the car. Those boxes are expensive from ford as i'm sure you know and that's why you bought a used one. A ford IDS can NOT change the mileage in that baclk box. Only Ford can do it internally and only on a new product. It's to keep dealers (OTHERS) and such from being dishonest. The only place that may be able to do it is Myairbags.com. Check with them.
SO if you want your gauges to match the pcm. You have to stop driving your car. Read the mileage in the pcm, Then order the new black box with identical mileage to the .9 or what ever it is and put it in before you move the car.