'01 Explorer Sport Trac - vibration from front

Problem with an '01 Ford Explorer Sport Trac V6. The problem I am having is at low speeds, between 5-15mph. The steering wheel and front end will thump and shake really hard, like something is or has come loose when I am making a turn. Almost feels like the power steering pump is giving out, but at higher speeds the steering feels and works just fine. The truck only has 70k miles and the belt on it feels good and tight. Power steering pump also has plenty of fluid in it. What do you guys think?

check the universal joints in the driveshafts, one may be binding... check the hubs if it has the auto-lockouts... one may not be releasing... may have a tire with abnormal wear on the inside edge...

This happened to my 95 Explorer and could swear that the problem was coming from the front. I would feel it in the steering. Took it to my mechanic and all it was was the rear u-joint on the driveshaft. Hope this helps. John