I wish it would be something as straightforward as the tie rod ends or the knuckles. Unfortunately that low hanging fruit has already been picked. Knuckles and wheel bearings are fresh and tight, as are the tie rod ends. The fact that the axle is shifting under the truck is a red flag. About a month ago I did a leg of the Georgia Traverse and had to stop because of how loose the truck felt. I ended up putting upwards of two full turns on several fasteners, including some of the u-joint nuts. I ordered new u-bolts and shackles from Kurt this afternoon. Should be able to get to it this weekend.