GMC Repair: 4x4 not working, gmc sierra, four wheels

Question
I have a 99/00 GMC Sierra 1500 5.3L. My front end doesn't seem to have any power if the wheels are on the ground. With the truck in the air all four tires spin but when I need the 4wd in the snow the front end does nothing. There were other problems as well but I replaced the 4x4 switch, transfer case motor, and front axle actuator. Any advice or suggestions would be appreciated.

Answer
Hi
So if I understand, with truck in air, and you engage the 4wd, all four wheels have power.
When you put it on the ground, vehicle only has 2wd, the front wheels do not spin?
I would think this would be internal mechanical damage in either the transfer case or
the front differential.
I really need more info if this is NOT correct.
Thanks