Shut off while driving, engine cranks but no fire?

Ok I will recheck on Fuse 20, but which sensor did you check the 5volt reference on and how did you check it? For example if you unplug the throttle position sensor (TPS) on the throttle body, turned the key On and only read 1.2volts (Brown/White wire), I would do the same for the next sensor you can get to which is the EGR position sensor (DPFE). If that sensor reads the same exact voltage reading as the TPS on the Brown/White wire, you are going to have to get to the fuel tank pressure sensor and unplug it as well. Its not easy to get to but you need to be sure this isnt a shorted out sensor pulling the 5volts down. I am kind of surprised you have any voltage on the reference wire.
Let me see if there is an easy connector to get to so you can unplug the fuel tank pressure sensor without having to mess around at the top of the gas tank, you can get to the plug but they are difficult. So if we can isolate that circuit by unplugging it somewhere easier that will help with any frustration. That 1.2volts might be the issue, I assume the battery voltage is ok, if its dropped below 12.4volts I would put a charger/maintainer on the battery while testing, or you will get skewed readings. And yes you should get a resistance reading, but checking resistance while a circuit has current running through it will give inaccurate readings, so you need to unplug components and circuits if youre going to do a resistance test on them.

I really only use resistance readings for checking components to have the correct resistance(to be within Spec), for a quick for short to ground test, or a quick continuity test. But for power and ground testing directly from a fuses source I will do an electrical load test so I am pulling more amps through a suspect circuit. A wire can test perfectly fine on a resistance test but only have 1 strand of copper left inside the wiring insulation. That situation will fail a load test using a higher amperage bulb. Anyway let me look for a connector for the tank pressure sensor.

Heres the location of the fuel tank pressure sensor, the 5volt feed to it needs to be disconnected somehow to verify its not the issue. You can slide under the truck and try to find the connector going to the top of the gas tank, it is possible with a mirror and flashlight to find the connector. But get it unplugged and see if the 5volts returns on the other sensors. I know its a pain, on these trucks I take the bed right off when I need to do a fuel pump instead of dropping the tank. But see if you can restore that reference voltage.
The last diagram is of the data link connector, you should have battery power on pin 16 and grounds on 4 and 5.
One last thing, is the battery voltage just dropping off after its had a full charge off the vehicle?

I should clarify this circuit load testing with a turn signal bulb. That is only for checking 12volt power feeds and grounds that come directly from a fuse or going to a ground that does not pass through a module. Its not meant for use on 5volt reference circuits. That was my mistake in not being more clear about that. When checking the 5volt ref, just use a DMM.
When you checked the TPS I assume you had it unplugged to check the 5v feed? And the same for the EGR position sensor, you checked it when it was unplugged? If thats the case, I would go back and unplug the EGR sensor, leave it unplugged and then recheck the TPS again, if the 5volts has returned to the TPS sensor, then the EGR sensor is causing the short.
The trick in explaining this is that they share this 5volts, so for example if the EGR sensor is shorted out, while its plugged in, it will pull the 5volts on the other sensors down with it.
Now when you go to test and unplug the EGR sensor, you are taking the short circuit away due to the sensor not being plugged in anymore. Hopefully this makes sense.
It would be the same if the TPS was shorted out, it would cause the EGR sensor to read low as well when plugged in. When either sensor is unplugged in it cant short the 5volts to ground.

The EGR, TPS and Fuel Tank pressure sensors are the ones that share that 5volt reference.
So for now just unplug the EGR and recheck the TPS. To be honest its odd that the TPS is reading 1.2volts and the EGR is reading 5v. I wouldnt worry about the tank pressure sensor right now. Concentrate on the TPS and EGR sensors.
This circuit is designed, internally, inside the PCM to handle a short to ground or shorted sensor(same idea). They do this because the manufacturers know sensors short out and they dont want to be replacing computers every time a sensor shorts to ground.
If you find the 5v return to the TPS with the EGR sensor unplugged, the truck might start. But see what you find, I think youre close to the issue here. That low voltage on the TPS is obviously a problem.

Yes and good diag work, plug the TPS in and see if it starts, it doesnt need the EGR position sensor to start, explaining how to test reference circuits can be very difficult on our end of things, so I am impressed. Hook the battery up and make sure it starts. When the PCMs go down due to shorted sensors like this, I dont think there is ignition spark or fuel injector pulse, so you shouldnt have to deal with cylinder wash from cranking when it wouldnt start.

On some vehicles that have lost spark for whatever reason, people tend to crank the engine excessively when trying to get it to start and this just floods the cylinders with gas and washes down the oil that should be on the cylinder walls, this, in turn, causes low compression. So hopefully it will fire right up.

The gas in it is not going to be fresh after so long, Im not sure how much is in the tank, if its low enough you can fill it up with fresh gas and it should be ok. Engine pinging or
pre-detonation is usually caused by carbon buildup. But bad gas can also be the cause as well. And you dont want to run the engine like that, it can cause valves to burn out or other mechanical issues. Basically what happens with pre detonation (or pre-ignition) is the air/fuel mixture is firing off before it should. Hence the name, this can cause intake valves to burn due to the mixture igniting before the intake valve is fully closed on the pistons compression stroke.
Another issue that I have seen happen a lot when vehicles sit for even 6 months is the fuel injectors become gummed up and either stick fully closed or just dont allow the full amount of fuel to flow. This causes a lean mixture (lean meaning a lack of fuel or too much air), a lean mixture also causes heat. Since this has conventional port fuel injection, (the good ole type of fuel injectors), you can pull the fuel rail and clean the injectors, the throttle plate, and Im willing to bet the EGR passages are probably carboned up as well. Id also add some fuel treatment to a fresh tank of gas. Drain the old gas if possible, because it will take time for the new treatment to start working,.
Of course an oil change is in order as well and use a Synthetic oil because it already has additives in it. But the fuel in the tank is most likely going to be the issue, unless youre hearing actual mechanical noise, such as a stuck lifter tapping away under the valve cover.
If you do a google search for "engine pinging and/or pre-detonation" it will come up with a list of causes and solutions. I assume this is not a lower end type of knock, such as a bad connecting rod.
If you want to clean the injectors really well, there is a tool you can buy thats about $40 or so that hooks up to the battery and will pulse the injectors for a certain amount of time. Just a couple seconds or so, but if youre interested in going that route I can explain what I do to clean fuel injectors when needed, the trick is to get things cleaned out as much as possible before having to run the truck for long periods while any other additives do their work. Sorry for the long post here, but Im really glad you got it running.
Here is one of our guides to engine ping or knock

https://www.2carpros.com/articles/understanding-and-repairing-engine-knocking-noise-an-in-depth-guide

As for the belt question, if you dont mind posting that as a new question that would really help.
But before you drain the tank, the engine pinging youre getting, is this happening right away when you start the truck or does it start to happen when its warmed up? Pre-ignition is heat related, and since I assume you still have the EGR sensor unplugged at this point? The EGR valve is there to reduce in cylinder temperatures when the engine is under a load. It will open under engine load allowing a small amount of exhaust gases back into the intake manifold, which then will reduce in cylinder temperatures. This helps to prevent NOx gases(nitrogen oxide), which is one of the combustion gases that pollutes the air. So I would replace the DPFE sensor and check the EGR passages to make sure there are no clogged ports.
I would also clean the injectors as well, since a lean mixture can cause engine ping as well. Id go through the whole truck, change the fuel filter, air filter, clean the throttle plates, the EGR ports, etc. Sitting for a year, things are definitely not going to be functioning properly. I have one of these old Fords we keep around just in case, and its basically the same setup.
There is a solenoid that controls the EGR valve, you will notice it has a vacuum line to it that goes to the intake manifold and then to the EGR valve. When the engine is up to temperature, if you rev the engine, the EGR solenoid should open and allow vacuum to the EGR valve, opening it. You can put a vacuum gauge on the hose going to the EGR valve and make sure its getting vacuum when you rev the engine.

Do you have a scan tool also that can read live engine data? A basic OBD2 scan tool should be able to do this no problem, the reason Im asking is to check and see how the fuel system is doing and how the PCM is responding to any air/fuel mixture that is incorrect. If the engine is running lean or rich you will be able to tell by some of the data PIDs. A data PID is a Parameter ID, such as a reading from a coolant temperature sensor, engine rpm, oxygen sensor voltage, etc. There are two data PIDs (Long Term and Short Term Fuel Trims) that will tell you if the engine is running rich or lean. A scan tool will also tell you if any other codes are set besides the DPFE sensor that is unplugged right now.
Since the tank is full, I just dont want to see you drain the entire tank and still have engine ping occurring. So taking care of these other components first, then see how the engine is doing. If the gas tank was lower, Id say just drain it, but being full, thats a lot of gas to waste. Some fuel treatment additive would be good as well. Again, I apologize for my long posts here.