5.2 magnum options

If you dont have a way to do a cylinder balance test, which drops one at a time, and compares RPM drop between each cylinder, an old track trick when your cylinder balance tester is back at the shop is put water in a spray bottle and with engine idling, spray water on plug wires, coil wire, etc. If you have a bad wire or cylinder, you will get a nice lightening show.

You can also pull wires off cap and loosely install them so with a well insulated pair of long pliers and engine running, you can remove each wire to see if it gets worse or doesnt change. Then you will know which cylinder to look at.

Get some carb spray or something that burns well and spray around intake mating surface, carb base, vac ports etc. Look for change in RPM as you spray. That will find any vac leak you may have.

The factory cams are not known for going flat as they are a roller. I would think more like broken valve spring or bent push rod.

Running worse when cold makes me think intake not quite sealing but expands as engine heats up. Look at intake gaskets to see if evenly crushed.