Vacuum leak?

[livingez_123]

I have been a ASE mechanic for my years until a back injury put an end to it. I have a 6.0 in my Denali and I have what sounds like a vacuum leak at 1500-2000 rpm. it's at part throttle and high vacuum. I ran the engine up to the whistle sound and soaked the intake and TB with cleaner hoping to locate the source. but nothing. I guess my question is...are the LS engines so air tight in the crankcase that if there is a slight leak in a gasket or O ring that it might produce a vacuum leak sound? Are there any common area's that might be prone to a leak?

I'm just an old wrench that is stumped on this.

 

[crazyikon86]

try spaying the booster, under the intake, and behind the intake. spary at idle not just when u hear it also

 

[GeneralNoobzor]

Sounds like the Intake Manifold Gasket.