Exhaust manifold heat shield. Possibly broken or missing a bolt. My 03 V8 has done this for a while. It's an annoyance but not a major issue. Haven't been able to visually verify because they are difficult to see. Mainly comes from the passenger side.

Changing the PCV valve won't hurt, it might need it anyhow. But it's not going to resolve the vibration. Nor would it have anything to do with spark plugs.

If you have what I have, it's a harmonic vibration that only happens at a specific RPM, in drive, at a stop light/sign or just sitting still for any reason. Engine mounts are next to impossible to tell if they are bad just by looking at them. The whole motor would torque over to one side if you had a broken one tho.

Check the AC lines on the passenger side and ensure you haven't lost any of the retainers and one is rubbing on something. Unlikely but more possible. Really, you need someone to sit in the truck when it's doing it and leave it in drive while standing on the brake so you can rummage around underneath to see if you can find it. Going to need to have the skids off too so you can see inside the engine compartment.