Recently had my Gm out in a field and got stuck. Engaged the 4x4 (both hi and low) but front end would not engage. Light does come on the dash indicated 4x4 engaged, but no grab in front. Couple days later, thought I would check it out on solid ground to try and figure out the problem, but engaged just fine and tested ok. Front end engaged perfect. Now the problem is touch and go. Sometimes works, sometimes doesn't. Light always comes on but doesnt always engage front end. Found that when I am shifting into 4 lo, slowly putting pressure until I hear the grind and then engaging works most times. Any idea my first course of action to get this under control? Thanks in advance.