Me too, leaning towards an injector.
as for other ideas;
This has already been talked about.
If you have COPs then swap the coils around.
If no COP then swap the secondary-wire to a different location.
If you have a distributor, check the #7 tower for cracks, tracks, or damage
If the misfire...
What I often do Is swap a different plug into the "bad" hole and see if it trips a code to whatever cylinder you put it into. If it trips in the new location. throw the plug away.
But if it trips in the same hole as it did before, then move the wire and/or the coil if COP.
If it still trips in...
I had a similar problem with my 08 Escape. There is a TSB on that. I replaced the vent line in the driver's side rear wheel well, and that cured it. I seem to remember that the end of the line was plugged with dirt or something. The new line terminates elsewhere. IDK, I forget. My wife rolled...
I think that is more a function of the rate at which the bowser is pumping, and the rate at which the air is escaping from the tank. Our pumps up here, Manitoba Canada, often trip the shut-off with those crummy small filler holes. Every car I have had, since they went to those, has done that...
You really need to check the fuel pressure, and or fuel delivery
I don't think there is a code for low pressure.
If your fuel pump is failing or the line is sucking air, then the engine will go lean, stumble due to misfires, and possibly stall; that is what sets the misfire code.
That NP435 is a HD 1:1 final drive trans, with, as you have found out, an extremely low non-synchronized first gear. That is a grain-truck trans, suitable for hauling heavy loads over soft dirt fields.
However, the other gears are not that bad and, the 1/1 final is the same as any other manual...
I would be leaning towards either a fuel-pressure issue, or a failing EGR system.
A scanner should reveal the problem, but without a code, you will likely need a good EFI technician to decipher the results.
The fuel-pressure issue could be as simple as the pump sucking air.
my big fat mouth has cost me a lotta money over the years. If I said I would do it, I had to do it. I'm a lot more careful what I say now. Actually, I learned to think things thru a lil better; "let your yes be yes and yur no be no"; I learned to say no.
Those old trucks are huge and heavy bricks and they take power to push thru the air, and the faster you go, the worse it gets. So if you really want one of those, you are gonna have to figure out how to make it take less power to push it thru the air.
Here is some help; the rule of thumb is that...