Do you know if the four wheel drive works?
I had a similar issue and could not actually get power to the front wheels - I would just get a grinding from the front end.  
My problem turned out to be a stipped axle shaft - in particular the short one on the drivers side - not a fun fix.
Best way to test is to lock the front axle (I'm assuming that you have manual hubs based on wording in your post), lift the front end of the truck.  If one of the axle splines is stripped, you will be able to hold one wheel stationary while rotating the other - you will hear the same grinding noise as it turns.
Passenger side axle shafts will pull straight out of the differential, the drivers side is clipped inside the differential, so you will need to pull pretty much everything off of the front end.