I found the results of the test with this truck from two years ago. Stock head and cam, and an open exhaust. It got through with NOx on the very high end of the scale, 5.5/6. So it seems that on my truck at least egr was not working back then.

HC was much higher on the motor, by an order of magnitude. It was old tired motor and that would be expected.

It might be reasonable to say that in a truck with a fully functioning emissions system the 261C will not push the truck into failing emissions. It may be causing a lean condition that is then causing high temps and higher NOx - that seems possible but I am not ready to make that claim just yet.

I find it likely that the bigger culprit here is the open exhaust and higher flow head. Again, back to my wrx days. Just swapping exhaust from the turbo back (downpipe to tail pipe) can cause you to run dangerously lean, on a far more advanced EFI system. And here we have high flow equipment, much higher flow than stock at least, with no corresponding adjustments to the efi system. I think that adjusting the AFM gears at least may be necessary in this scenario. I would think the ECU would learn the new setting and adjust in closed loop, but in WOT open loop? That is where I want more fuel put into the system.

I think a wideband o2 is in my future.