My test did come up negative but I think you found the leak! As HeyYou said change them all

 

Thanks HeyYou. Just realized you are an admin.

I will definitely test without O2 sensors this weekend when I do the freeze plug(s).

I did some more research and it seems like that loss of vacuum when pressing the accelerator is normal. I’m beginning to think that maybe there is no power loss and it’s just a heavy truck with an average motor and a suspect transmission lol

Any thoughts on the surge at idle? It only happens when warm. I was thinking it’s a weak fuel pressure regulator. It has a slight hard start after sitting overnight, but fires right up throughout the day. Since the FPR acts as a check valve, I was thinking that the surge is from the FPR losing pressure at idle, fuel retreats, the rpms drop, the IAC adjusts, the resulting slight rev gets the fuel pressure back to spec, and repeat…

 

Check fuel pressure. A surge at idle could mean many things. I would start with fuel pressure

 

Fuel pressure was to spec. Steady needle from start to warmed up idle and with throttle engaged. Never budged. Spot on 49 psi.

Going to use one of these for the freeze plug tomorrow morning:

If I get everything else sorted, leak down test, exhaust, etc, and the engine ends up being worthy the extra effort to put in the brass ones, I will. For now, I’m more than happy to report on how this holds up…

Slight rough idle still. When in Drive and at a stop, it doesn’t surge, but it does have a slightly rough idle holding steady at 600 rpm. In my driveway, while in Park and especially Neutral, it definitely surges from 650-675 rpm at a very steady rhythm.

Might put the original MAP sensor and TPS back in and try a Dodge IAC.

 

Likely not the IAC. I would more suspect a slight vacuum leak somewhere.

 

Does anyone know if there is a diagram/list of the vacuum system in the manual? I can't seem to find it for the life of me.

 

You can test the cats with an infrared temp gun. Good videos on doing this.