When I bought my spare parts truck I was told by the P/O the  tranny had a no reverse ... would sometimes sound like it was trying to engage.
  The trucks would need some more work to make it drivable, so I can't verify the tranny issue .... but I could work to get it drivable if "curing" the tranny issue resulted.
  Anyhow, what I do know is it won't crank over in park...has to be pulled back at least to the reverse position.  So I guess the park interlock switch is out of adjustment.
  Question: Is that on the shifter inside or down on the tranny somewhere?
 And, more importantly, is it possible the park switch and/or linkage missadjustment might be the reason the tranny won't go into reverse?
  Anybody have experience with a4ld linkage adjustment? It's a shifter on the floor/linkage/pushbutton 4x4 on dash set-up.
 The has no body lift kit or anything to make adjustment weird or whatever.
  Thanks guys, dave