2003 GMC van with a 5.3L vacuum

[byopautotire]

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...

[carriedi]

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?

Other than the sound, how is the engine running?