Open your driverside door, you'll see a sticker on the door jamb. Look under where it says AXLE. What's it say?
Another place is to get under the back of your truck and look at the differential cover and you'll see a tag on the passengerside...what's that say?
Take those numbers, and there's a 'stickied' thread at the very top of the section you posted this thread in. Decode the numbers.
'01 XLT disguised as a '03 Fx4 Level II.