2005 Tahoe Stuck in 4WD
 

My 2005 Tahoe is stuck in 4WD. When I move it to 2WD it drives for a few hundred feet and then its almost like being in nutral (I press the gass and it does not go). I then hear a winding sound. When I press the 4WD button, it goes into gear and begins to move forward again.

I once parked it in 2WD, but when I got out my truck began to roll :eek:. Any ideas???