My 03 Z71 with 255k miles has an issue with the driver side rear view mirror, I push to move the mirror, moves, then resort's back to it's original position. I don't know why

 

At this point I don't know why, but maybe some answers might help.

When it goes back to its original position, do you hear any noise as if the motors are moving it?
At least we might get some idea of a module with a possible back circuit problem.
How does the other side behave?
Can we tell if there is something inside the mirror assy that is being stretched or pressured to return to original position?
I believe if we might be able to get some of those answers we might be able to offer a useful suggestion, what do you think?

 

You could disconnect the mirror's electrical harness, but you need to remove the door panel to do that.

 

Setting in the drive way, it now works.