Just found this post. My truck was doing the same thing for a while. Then it started making a noise that sounded as if I were driving on a rumble strip on the highway at speed.

Right wheel bearing had some play in it, and solved all the problems. VERY easy job, just did it this weekend. Turns great in drive and reverse, and both in 4wheel.

Mine would feel as if the wheel would just stop as you were slowly turning. Scary feeling. But the wheel bearing fixed it.