300 4×4 steering

I have a problem with the steering on my 300 4×4. At times in 4 wheel drive the steering gets hard to turn. If I go into 2 wheel drive, back up and put it back in 4 wheel. It will work again.
I read or heard somewhere, it was the oil in the hubs. I changed the oil and made sure they were full at 4 o’clock position.
Any help?