I doubt this is your issue judging from your avitar as your truck doesnt look lifted......but i thought i would throw it out there just in case...
Lifted trucks wit aftermarket drop pitman arms have a lot of issues with the nut that holds the pitman arm to the gearbox loosening and causing steering issues.....its a 1 7/8 nut so it takes a big wrench to do it without pulling the gearbox...and the torque is pretty high (i dont remember off of the top of my head but i beleave over 200 ft/lbs...)