Sept PO300, April 2022, P1404, April 26 PO302 and c121c

Hello, your question is a little bit difficult to understand, but I will explain the codes you have. The P0300 is random cylinder misfire, and the P0302 is cylinder #2 misfire detected codes.
The P1404 code can cause cylinder misfires, it is EGR valve Position Sensor Rationality Closed. The EGR valve is used for emissions purposes to keep in-cylinder temperatures down. The EGR valve has a position sensor on it so the engine computer (ECM) can know if the valve is open or not. So, the wiring to the EGR valve and voltage readings need to be checked. The valve has five wires to it. Three wires are for the EGR position sensor and the other two are to control the valve itself.
If the valve is stuck open, you will have stalling at idle but should smooth out when at higher rpm because that's when the valve is supposed to be open.

The water pump absolutely should not have been glued on. The bolts should have been drilled out and then the bolt holes should have been re-tapped with new threads for new bolts. That will cause you problems. Glue will not hold the water pump on.

The (C121C- Torque Request Signal Denied) is the reason why the Traction Control light is on, and the Throttle light is flashing. One light may be on and then the other may come on. This is because the engine computer cannot determine why it cannot gain control over Yaw/Traction control system. This is a manufacture specific code. There are a number of reasons why this may be happening. Due to the other code P0302, this code may be part of the issue. Misfiring cylinders and other codes that have to do with engine control such as the P1404, P0300, P0302 all have to do with engine control. These other issues need to be repaired correctly first. If the engine computer cannot gain full system control due to multiple faults like this, a code like C121C can set. Basically, it's the engine computer telling you it has reached a limit where there are too many faults occurring at once and it cannot control the engine in the proper way, and it will deny other systems to function correctly.

The cylinder misfires can be caused by that EGR valve not being fully closed, bad sparks and regular tune up parts. Each cylinder should be checked for performance, the EGR valve needs to be diagnosed, and the water pump needs to be fixed correctly. The C121C code may shut off by itself if these other systems are corrected.
I would also have the throttle body cleaned. The last guide below has to due with cleaning the throttle bore for carbon deposits.
The vehicle is probably going into Limp Mode, which is a failsafe mode and that may be why you can't get above a certain speed.
I'm not sure why the mechanic didn't address all these issues. I would take the vehicle to a shop you trust and can do the work correctly.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/how-emission-control-systems-work

https://www.2carpros.com/articles/how-a-car-computer-works-pcm-ecm-bcm

https://www.2carpros.com/articles/throttle-actuator-service

Okay, I'm having a little bit of trouble with what you're saying, but that's okay. So, it sounds like you took it to AutoZone first? I know they can tell you what the codes are in the computer. And are you saying that you have purchased those components already, the PCM, crankshaft position sensor, EGR valve, and fuel injectors? All I can see on the picture is " Computer Diag, Has Valvetrain problem, and something about carbon build up. If you could get a better picture of that so I can see the whole thing. Sometimes picture from customers don't come out to well over the internet, but your question about the "valve train" is. The valve train is the upper parts on top of the cylinder head under the valve cover. So, this will include the camshaft, the intake and exhaust valves, valve springs, and rocker arms which open the valves. And I think what he was saying on there is a build up of carbon deposits on these components will affect the performance. Carbon build up on the intake and exhaust valves for example can cause them to not open fully and/or hang open when they should be closed. You may hear a lot of ticking type of noises with valve issues.
Also, a lot of carbon build up under the valve cover (same area) can restrict the flow of oil to those components preventing them from being properly lubricated causing extreme heat build up and other problems.
As for where to take the vehicle, for one the people at AutoZone are not mechanics. They can only tell you what codes you have, and usually they will just sell you the part there is a code for. This is not the correct way to diagnose an issue. A code only tells you what the engine computer is detecting as a potential fault.
The dealership is going to be the most expensive option. And you are correct, it is difficult to find an honest shop. I don't think you need to replace the PCM, I think these other issues just need to be addressed first.
The carbon build issue is probably what is causing the most of the problems. It will cause cylinder misfires, EGR valve issues, etc. If you can get a better picture of that invoice up there that would help.
Also remember that if the cost of fixing the van is more than it's worth in value. Then you might think about finding something newer/used.
So, try to post a better invoice picture and we'll go from there. You can go to a couple of different shops and show them the invoice as well and get different quotes. You will notice a difference for sure doing it that way.

What information did you not receive?
Okay, on the second invoice it looks like all they did was hook up a scan tool and read the codes. Only says "Code P0301 cylinder #1 misfire" and has Valve Train Problems, Possible carbon build up.
Thats not a diagnosis, that's a guess at best. And then a $75.00 diagnostic fee.
Both of these are awhile back too. It doesn't look like they did any testing at all.
So, you took it to AutoZone next and then that's when the P0302 and C121C showed up?

What do you mean Heater 2 circuit and "also secondary"? Are you meaning the Oxygen sensor?
The P0403 is an EGR "circuit" code, which means there is a wiring issue to the EGR valve. Since you already replaced the valve and gasket, there must be a wiring issue. But I don't think a non-functioning EGR valve will cause the issues you are having. The P1404 is an EGR valve closed code.
With all these issues and you have already replaced the spark plug and wires twice, the crankshaft position sensor and the EGR valve and you're still having stalling/running problems then there is something else going on here.
There might be a problem in the wiring harness and that's why you're getting so many different codes like this.

Any code that has "Circuit" in it is usually a wiring issue or the engine computer detecting some sort of voltage issue. So, if there is a wiring issue to the EGR valve and the valve is not being activated, that's what is causing the 2nd code P0404. Below is a picture of the EGR valve and where it is. The wiring to the valve will need to be checked, since it's a new valve, the tubing to the EGR valve may be clogged up with carbon build up, or it has a wiring issue, and it is not able to be commanded on.
Below is a video of a 2005 Dodge Caravan but it has the same EGR valve that yours does. He is showing how to test these valves.

https://www.youtube.com/watch?v=Ty29y3R8fZI

It's in a different spot in the video but it is the same type of valve. The valve needs to be checked for certain voltages. Do you have a multimeter to check the voltage readings at the harness plug for the EGR valve?

https://www.2carpros.com/articles/how-to-use-a-voltmeter

It's not a part, it's a tool for reading different voltages. But if you have no experience in electrical work on vehicles it's going to be very difficult for you. Do you want me to just explain what you should say to a shop if you stop at one? Since you have the invoices from the other shops. You don't need to look for a specific water pump mechanic. You just need to find a decent shop. Just explain what happened with the water pump and that you need them to diagnose the EGR Valve for the P1404 code and that's all you want done. Tell them the EGR valve is setting that code as well as the P0403 and P0404, because they are all related.