Shouldn't be any play in the pitman arm but I doubt if that is the source of this problem. This problem being that bad is going to be one of the following.

Trac Bar: Crawl under there and have somebody turn the sterring wheel side to side to see if there is any slack in the movement. If so it's bad.

Front Sway Bar Links: I never knew this before but after a conversation with the guy that developed the DT Profab trac bar he says that the sway bar is a major source of steerng problems in these trucks.

Front Wheel Bearing: Jack the truck up and without pulling it off the jacks try to move the wheel around. Any play in it is a bad thing.

Ball Joints: While the truck is up put a bar under it and see if you can lift the tire without moving the truck.

 

i got a bad wheel bearing, it squeaks so much on bumps and turns, i need to fix it soon