2001 F150 SuperCrew 4wd 5.4 triton

I'm not a mechanic, but my brother told me I should drive a little in 4-wheel drive for lubrication purposes. When I put the truck in 4-wheel drive high, the rear driverside wheel appeared to have problems turning, as it was scooting across the grass. Is this a potential problem with the 4-wheel drive system? or maybe something needs lubricated? thanks for any help