I have 2 questions re: 4WD - First, can I push the button while driving to go from 2WD to 4WD? Second - I have noticed that when the 4WD is in the lock position, and I making a tight turn. such as a u-turn - the wheels "stutter"...hard to describe other than it makes a series of quick jerks like a stutter. When I straighten out it is fine. Is this normal?