My first magnum build, advice appreciated

First thing I would do if it’s all stock is make sure that the plenum gasket on the bottom of the intake is not leaking. Very very common problem on the factory keg intake. If it hasn’t been replaced, I’d almost bet it’s leaking. Open throttle blades and look into the bottom of the intake and if you see a lot of oil or puddling it’s leaking. It will use oil, cause crappy mileage, valve ping and a loss of power.