Engine Idle Drops A Lot in D
This PCV looks like a standard Mopar PCV. As such, it will have a transition vacuum level from the low idle flow to the high cruise flow at about 12-14 inches. If you have an idle vacuum of around 10" in D, then this PCV is wide open to cruise flow level, and that is essentially a moderate vacuum leak. If the RPM's go up when in P, then the vacuum level will go up and the PCV will transition to the lower idle flow, and the RPM's will rise even more; it feeds on itself to push the PCV past the transition point. Your idle symptoms are spot on with this issue.
This is a common issue with the stock Mopar PCV's: it's the wrong PCV valve for even a moderate cam. Pinch off or block the PCV hose leading to the carb base as a test and I bet you will see the idle RPM's in D jump up 100-200 RPM. That is a sure test of this being an issue.
Regardless, of what other things are going on, you need to change the PCV; it is part of your problems here. A Fram FV 191 has a lower transition vacuum level that is appropriate for this cam, but is not a direct physical fit. Do this before you make other changes, or you will have to go back over everything again once you do fix the PCV.