One of the nice things about 4WD is that you can remove one driveshaft and see if things get better. I don't have the AWD model Explorer, but I would think that a 10 mile or so test drive would not be a problem with the AWD model. Take the front drive shaft out and go for a ride. It is an easy removal (less than 30 minutes and most of that time is getting the truck up on jack stands and back off).

On my truck I removed the front driveshaft and could tell that the "clunk-clunk" went away. So trouble shooting was over.

I have also replaced the two CV 1/2 shafts on the front end several months prior to the driveshaft. I was getting a little poping sound in parking lots and my ride was getting rougher. I put both axles on jack stands (all 4 wheels off the ground) and at a low engine speed put it in gear. The right front wheel would slow down and the a little pop and it would speed up.

I replaced both CV 1/2 shafts at the same time.

The reason I bring this up is that some front end "clunking" could come from the CV joints in the 1/2 shafts and not from the driveshaft.

Regards ............ John