^^^^^ THIS ^^^^^Do NOT shift from 2WD into 4H if you are spinning your wheels though.
If you are accelerating &/or spinning it could cause damage. Your speed isn't a major issue if it's bad traction you shouldn't be flying anyways.
Do not attempt to make a shift while only the front or rear wheels are spinning. The front and rear driveshaft speeds must be equal for the shift to take place. Shifting while only the front or rear wheels are spinning can cause damage to the transfer case.
Shifting effort will increase with speed, this is normal. During cold weather, you may experience
increased effort in shifting until the transfer case fluid warms up. This is normal.