I changed the upper intake gaskets properly and changed valley cover gasket however it still sounds as if there is a vacuum leak! I checked the vacuum lines which aren't many, all of them look good. I do know that when I accelerate it sounds as if the leak goes away! but it has a hard time shifting gears in the transmission! Please help if you got an ideal, I am ready to breakdown...
To find a vacuum leak, I use a stethoscope with the sounding drum off so it's just a tube that I can listen through and try to find where the sound is coming from. I also use a propane tool that has a tube and a small pipe that can let propane gas out and move that around to see when the engine sucks in the propane the engine speed will react.
you could also use a scanner to see if you have a vacuum leak by looking at your fuel trims at idle.
It's possible that you may not have an external vacuum leak. PCV valve whistle?