I know the magnums had a problem with the pan on the bottom of the intake leaking causing vacuum leaks and oil issues.

It could be causing a lean condition. Open the throttle blades and look into the bores with a flashlight. If there is excessive oil on the floor of the intake it may need a new pan gasket.

I prefer to replace the factory sheet metal pan with 1/4" thick aluminum plate. I can buy it apiece of aluminum and use the original plate as a template to drill the holes. Best of all, it won't leak.

Several companies sell the prefab plate but it costs more than if I make it myself and it only takes about 20 minutes.