so I go to put my truck into 4x4 and I lock the hubs and when I pull the lever into 4H it doesn't set into place. I can drive for about 20 feet then it pops out of 4H. help please? its an automatic

 

I would suspect the shift fork in the tcase has broken/worn sliders. I've only dealt with BW13-56 cases, and I'm not certain which case came in that truck. Someone else will chime in with more concrete diagnostics.

Edit: I'd also look at the shift linkage outside the case, between the lever and the case. Make sure it's tight. If its loose, see if you can manually shift the case into 4x4 at the case (not using in cab lever) and see if it stays in 4x4.

 

Tough one, I'd start with the lever mechanism itself, there is a shift gate mechanism on the outside. Make sure it's working, adjusted, the lever isn't being hit by the body, etc.

If it looks ok, shift it into 4H then remove the lever mechanism. Then try and move the shift rod by hand, does it move easy, does it fall into a detent position that it wasn't in, etc. Then drive it to see if it stays in 4H with the lever removed.

 

I got under there and messed with the linkage and levers and now I can get it into 4H by pulling back and shaking it from side to side a little bit. I will check some other stuff that takes more work to get to this weekend when I have time. thanks guys for the help