Some of you who thought that I shouldn't be so skeptical about if the 2 speed would work. Well I'm eating my words now, cause it works! I used a hand vacuum pump on the rear diaphragm housing, jacked up the rear and had a friend turn the drive line while I put vacuum to it. I knew right away that it should work because the vacuum gauge was reading good numbers and then that beautiful sound...."CLICK". That was the sound of satisfaction. Now the sound isn't loud and the sensation my friend should have felt was subtle. What was the absolute was when we only completed the shift half way and turn the drive shaft was doing nothing. I had a split second fear that we may have broken something. I added vacuum again and "CLICK" it shifted. Thank you GM for making quality parts and I'm apologize to all of those I doubted.