when shifting in/out of 4 low, shift transmission to N and reduce speed to 2-3 mph. then shift hard and fast from 4hi all the way through N to 4lo. do not shift slow, do not shift easy, do not pause in neutral. just jam it and it'll shift fine without grinding.
if you do pause in neutral (i told you not to), then since there are no synchronizers, you'll be stuck there and it'll grind like crazy going either way. then you'll have to turn the truck off, finish the shift, and start it back up.
as said above, the binding and hopping in 4wd is normal. so don't drive in 4wd on hard dry paved surfaces or you'll put a lot of stress on the driveline. in dirt, mud, snow the driveline bind can escape easily by spinning a tire a little bit. when in 4wd on hard dry dirt, it can be hard to make a sharp turn, and requires a little stopping and backing up.