This is the second Ranger I have owned that has had this issue. First one was a 2000 XLT 4x4 with 117k miles (auto trans). I found out it had to be rebuilt after trading it. My current Ranger is a 2002 Ranger XLT 4x4 automatic trans.. On take off you can feel it clunk because of the delay in the rear diff. The shop was able to recreate the symptom on the shop lift.

I had them pull the rear differential cover and there were metal shards and the pins had play in them. I found there is a recall for Manual trans Ranger for this issue but not the auto trans. I seriously doubt they used different parts supplier for the rear diff between the auto and manual trans models.

Another complainant on this site said he was able to check the part number and that it is the same part as the Manual Trans models. I also test drove an 2005 Ranger (55k miles---would have bought that one but dealer wanted too much) and it had the same clunk (that makes 3 I have personally seen). Ford was once known for making the best trucks...