Don,
1. When you are shifting your range selector and it doesn't immediately go into gear easily, just touch your forward pedal very slightly while selecting your range. This works nicely on my 4100.
2. I suspect you are turning or have just barely completed a turn, or you are on a dry hard surface when trying to disconnect from 4WD. Make sure you have straightened out for a few feet, and/or try to disconnect before going on a road or other hard packed surface. It's related to what they tell you in the owner's manual about where to use and not to use 4WD. See if this helps.
<font color=green>Duane</font color=green>