gear ratio of rear on a 2002 mountaineer
 

I am totally lost. I called the ford dealer and gave him my vin number and he said it was a 3.55 gear ratio for the rear axle diff. But on the inside of the drivers side door it says D4 and D4 is to be a 3.73? so i am totally lost. also if i look the vin up online it says it's a 3.55 gear ratio so i am confused with the door tag saying D4.

I need to replace it as it has a dead spot and was making banging sounds as driving. you can jack the car up put it in neutral and have someone hold the drive shaft and turn the tire without the other side spinning in one spot.

If you look at my door tag there is a 45 on it but it's in the spot of the country code right above the axle code area. could someone of entered info in wrong for the vin since it has a 45 so close to were the axle code is? the tag on my rear is rusted so bad that it's breaking and you can't read it.