1998 Chevy Z71 4WD lock-up problem

I have a 1998 Chevy Z71. When I put it in 4WD, if I attempt to make sharp left or right turns, the truck will lock up and refuse to move.  I hear groaning and scratching sounds, but cannot locate the source.  If I keep the wheels fairly straight, it drives fine.   The only way to fix it is to take it out of 4WD and straighten the wheels.  

I was given an opinion that the front spider (pinion/side) gears are broken.