2003 Chevy 1500hd 6.0l Vacuum through oil fill so bad it’* very hard to remove the oil cap while the engine is running. Iv replaced the pcv but still have the same issue can some one point me in the right direction please

Intake restriction? Gasket?

I wonder if a PCV tube is plugged.

I’ll have to look into that

when I pull it out while it’* running still hooked to the tube I can feel it sucking air through the pcv

Suspect the intake gasket.Have seen them leak internally especially if it still has the orange one.

I am not familiar with this application, however if the PCV doesn't seal properly, this can also cause this. If it requires an O-ring, and doesn't have it, or it'* in the wrong place on the valve, it could cause this also.

I replaced the intake gasket and valley pan gasket since I was right there. This did not fix the issue. Still sucking hard. Pcv tube not clogged. While running I pulled the pcv out and the sucking through the oil cap seemed to calm down. I noticed that the intake had been swapped out at some point to a doorman intake could this be causing my issue? Different plenum size the oem?

Maybe, however, if it is a Dorman it is probably made to factory specs. The only question left related to this discovery would be if someone put on an INcorrect Dorman replacement intake that has a vacuum path where there shouldn't be one.

there was only 2 lines plugged into the intake one line going directly to the pcv and other going directly to passenger side valve cover