I understand this post is more than a few years old but I am posting in hopes to help out someone going thru this. I have a 2002 and ordered from O'Reilly, AutoZone, Discount and NAPA. They all assured fit but none worked. They advised to buy entire rear assembly quoted roughly $1200. My final attempt before putting that much money on a 16 year old truck was to call Powertrain Industries. Provided them the discontinued part #F75Z-4800-BB and they shipped a part that they said would fit. The appearance is slightly different but it worked like a charm. Downside is there is no warranty for the part, cost roughly $110 with overnight shipping. There is a dust shield came off after first week, but is not affecting functionality.
I know its old but I freaking love the truck and dont really want to get rid of it.