An easy way to see if its your auto-lockers is to jack up the front of the truck and get both wheels off the ground. With the truck in 2wd, you turn the front driveshaft in the SAME directiona few full turns, You should feel a click and it should get harder to turn. If it gets harder and both wheels are turning your auto-lockers are good, If one wheel spins and the other doesnt, the non spinner s the culprit. On mine it was both sides. The swap took no more that 30 minutes for both and seem to be better if you get stuck, because as soon as you lock them and ht 4x4 button you are instantly in 4x4, not like the auto's where you need the truck to move a certain distance for them to lock, if your really stuck and can't move at all you will never get into 4x4. Just another plus for manuals.
Emerald