[Mykk]

Those Vortec 350's are known for intake gasket issues, mostly due to dexcool. Felpro has a revised updated gasket for the application.

That intake gasket separates coolant and oil from air/fuel. I would first replace the intake gasket and go from there.

If your not satisfied after that, do a compression test on all cylinders (for comparative figures) and the coolant test strips.

Cheers ~Mykk