I'm about 90% sure that my plenum gasket is smoked, planning on getting the Hughes kit and all new gaskets and bolts and getting it done here pretty soon. But to make sure that is what's wrong, I'm taking the truck to a friends mechanic shop tomorrow. He is going to do a smoke test on it, will the leak from the plenum show up?

 

No. Just get a TB gasket and a small mirror. Remove the TB and look all around inside for oil pooling.

 

Well I already did that and there is oil pooling... so why do I have a huge vacuum leak then?

 

I heard that air will leak through the plenum gasket if it's screwed up and my truck has had an air leak for a long time now

 

If the oil is pooling then the gasket is blown and you have an air leak.

 

^^ As said above...if you have oil in the manifold, then your plenum gasket is ruptured. No need for a "smoke test". That is also your vacuum leak.

 

if there is oil in there pooling up then you need to replace the plenum gasket. simple fix!! do it. i did mine 4000 miles ago and when i did the oil change it was still full of oil i lost nothing. gained 2mpg as well!