I thought I read that the gen 4 exhaust manifolds flow better than the gem 3. I've looked around but can't find where I saw it. Can anyone confirm they do? I have broken manifold bolts and figured if I was fixing them I would just throw on the newer manifolds too.

 

They all look the same to me minus the lower flange differences of o-ring vs donut seals and the early egr ones.

 

Same manifold no difference 99-2013 '
no difference 4.8-6.2 same exact manifolds.

 

I would gasket port match the headers if you had them off. My 6.2 factory manifolds had over 1mm of soot stains in some exhaust ports.