Bad misfire cannot drive

[oldsman003]

Hey folks, i have a terrible problem. I own a 2004 Yukon XL 2500 4x4 6.0 200k miles, I purchased the truck in April for a tow vehicle, I have horses. Towed great at first. seemed under powered but figured was normal because i made a transition from a 12 valve Cummins dually to this. But then became obvious that was not the case. started to struggle with 10k pounds behind it, then started struggling with only my empty 3500lb trailer and quickly got bad enough i simply cannot drive it anywhere. all within 3 weeks. Very quick downward spiral.
Now it misses on every cylinder on bank 2

Steps I have taken in the attempt to fix this

I have replaced with new or used but proven working condition parts
-throttle body
-crank sensor
-cam sensor
-map sensor
-vacuum sensor
-PCM
-MAF sensor
-air box (has afe, replaced with stock and back no diff)
-acdelco plugs
-champion wires
-coils
-injectors
-replaced and added larger sized engine grounds
-o2 sensors

A mehanic hooked it up to a tech 2 tuner and could not find the problem, advised me he thought it was a burnt valve, I pulled the passenger side head only to find this engine is a fresh rebuild that still has hone marks in the cylinders, so clean you could eat off of it.

My cats were clogged and at the moment are cut off waiting for replacement after truck gets running right.

I am baffled at this issue and am tired of throwing money at it, and it seems I cannot find anyone who knows anything about anything.

I have tested fuel pressure and compression fuel psi is a solid 61psi at the rails and every cylinder pushes between 110-125psi on my gauge.


HELP PLEASE!!!!!!!!

 

[PLUMBDUMB]

I had a similar issue with my 99 Tahoe. It was stuttering and losing power eventualy backfiring and then not running at all. I tried a bunch of things I had a bunch of different guys come over and try to help me out we tested numerous things and in the end turned out to be a bad cap ( cap and rotor).