Hey guys, update. (I hope this thread isn't too old HeyYou, just let me know if you want me to create another one)

Replaced the o2 sensor before the cat, the truck was running great since my last post. No codes, no misfires and power seemed to be back where its supposed to be. This morning my misfires came back. Random misfire on 5,6,7,8. Truck shakes back and forth badly when approaching 40-50 MPH unless I gun it from 30.

Took the truck to a reputable muffler shop here in town and had them pressure test the cat. They poked a hole before the cat and a hole after the cat with a torch and the flow between both holes was exactly the same. The tech there said he was unsure if there was anything inside of the cat, he mentioned that it could potentially be hollow. I would have to stick a rod in there myself to check but I don't think that could be it?

My code scanner shows the Catalyst monitor is OK but htd catalyst is always N/A. Should I just have the shop cut it out?

Not really sure where else I should be looking.

 

IF the cat is hollow, just leave it, and don't worry about it. (and updating this thread is fine. )

How do your plugs/wires/cap/rotor look? What brand/style plugs?

 

Cap/Wires/Rotor - Cap and Rotor Wires replaced 12K ago: - Replaced wires again less than 300 miles ago https://www.rockauto.com/en/moreinfo...935&cc=1314563

Had plat plugs for about 10K and ran into an issue about 11K and took your advice to replace with copper. I put NGK - G-Power copper plugs in less than 1000 miles ago.

Checked for vacuum leak at the plenum checked side gaskets for oil and the pan (heughs aluminum plate). Checked voltages to the crank position sensor. Inspected the pickup coil (thanks to you for elaborating in another thread the pickup coil is the "CAM position sensor" I did not know that) No oil around the connector and it didn't look bad, almost unused.
Replaced pre-cat o2 sensor with NGK because I was getting a bank 1 sensor 1 slow input.
About 12K ago replaced all injector O-rings. Not leaking fuel, new fuel pump 12K miles ago, pressure at rail is good.
No coolant loss that I can see stays about the same

Some things I noticed today that may or may not have anything to do with anything:
It does appear that I have a small oil leak by the back of the oil pan. I wonder if I up shaved the rear main seal and its leaking, but I don't think that would cause it? Its not a bad leak.
When the truck is off, if I press the break the dash lights come on, if I let go they go off. There are a couple of cuts in the trailer cables I think its on the same wire and its grounding out maybe? I suppose I can just cut the cable as I knew I had to replace this.
There is some white power (battery acid?) forming on the positive battery connection. Not on the battery terminal but the round battery connector. Not sure why, that's new to me.

I have not replaced the Ignition coil - It looks a little worn and I have not checked the voltages. Maybe pick up a decent Spark Tester, I hear the light bulb ones do not work well.

 

I would be looking real hard at the crank sensor......

 

Mine had a similar issue, it was the TPS sensor.