(Insert Fiber/Bran Joke Here)

So, when I bought my 04, it had a slight humming noise at part throttle at about 45MPH. I didn't care to iron it out before I bought it because I had already sold my other vehicle, and the truck also came with a 6/75 Powertrain.

After three months, I sent it in to have it looked at. They determined what I figured... the pinion depth was not right, and it needed rear ring and pinion replacement.

All was fine, and I was quite happy with the service... but...

We've only taken it out once, and I noticed that the mileage was terrible and that at only 63MPH, we were passing everyone like they were standing still. I had heard of this happening on another vehicle once, so I figured the diagnosis would be easy... I first checked the mileage against the mile markers on the road. It was off by 10%. Then I drove it onto gravel and put it in 4WD... sure as heck, the front wheels were chucking and getting pushed by the rears.

If my calculations are correct, they put 3.42 gears in instead of the 3.73s.
That would also mean that at 63, I was actually doing about 70... no really officer, I wasn't even doing 65!!! That would also explain why my mileage was off by a little more than 10%. I'm glad I found out before engaging 4WD at 50MPH in the winter.

On the work order, it stated that the gear set was 5L3Z-4209-D (first set of numbers are for an F-150, but same thing, right?) . It's either the wrong part number, or the wrong gears were in the box. Anyone happen to know the right number for 3.73 gears for an '04 Expy 4X4?