Hello James B,

Test your catalytic converter the easy way: https://www.youtube.com/watch?v=qJTmddbOxMk (3 psi MAX back pressure)

I have zero mechanical knowledge and can't fix anything without breaking it first; but try this:

Spark Plugs -- REMOVE & INSTALL ONLY ON A COLD ENGINE & USE PLENTY OF ANTI SEIZE ON THE THREADS (WHY..?)
Spark Plug Wires -- REMOVE & INSTALL ONLY WITH THE SPARK PLUG TOOL DESIGNED FOR THIS JOB (NAPA HAS...)

My truck likes 91 octane gas & fuel treatment to keep cleanliness in the fuel system & lubricate cylinders...