Lower fuel trim with weak power and slowed speeds?

Hello, you're thinking about the fuel trims backwards, with a long term at -14%, the ECM is taking fuel away from the mixture due to what it is determining to be a Rich mixture not lean. Where did you buy the fuel injectors? This is becoming a more common occurrence with people buying cheap fuel injectors that are not the OEM injectors, it sounds like the injectors you may have purchased are flowing too much fuel, and the ECM is taking fuel away to compensate for this issue. When you look at fuel trim numbers, that is the action the ECM is taking to deal with a fault, not the cause. So if it was +14% for example, it would be adding fuel to deal with a lean mixture and get the air/fuel ratio back to 14.7:1.
Without doing a fuel injector balance test, you wont know if there were injectors flowing more or less than the others.
What was the original issue that made you replace the injectors?

The fuel trim value will come back down towards zero again when the issue that is causing the rich condition is taken care of. Think the of fuel trims as the ECM telling you what it is doing right now. So it is telling you that it sees a rich mixture (too much fuel) and it is taking fuel away to deal with that problem. I do see all the dirt around the bottom of the injector seals, I would clean all that as well as the holes where the injectors sit, use a vacuum at first if possible so you don't get anything failing into the intake manifold, and make sure those seals are cleaned as well.
Why did you replace two injectors to begin with if the fuel trims were close to zero? At this point since cylinders 2 and 3 are setting misfire codes, I would replace the seals, clean it all up and see if the fuel trims come back towards zero. You have to make sure all the injectors and the fuel rail are seated correctly, be sure they are all down. It can be difficult with dry injector seals, some manufacturers will tell you to use a very small amount of mineral oil on the seals to help them seat down fully.,
here are some guides to help with testing and replacing them if necessary, but I think this is more of a self inflicted type of scenario where the codes are setting because they weren't seated down correctly. It sounds like the middle of the fuel rail was not down all the way when cylinder 1 and 4 were fully seated.
But if the codes come back after getting them seated correctly, I would follow the testing guide below first, you need to be sure this isn't also possibly an issue with loose pins in the injector harness connectors or damaged wiring.
And an injector balance test is where you would have a fuel pressure gauge on the fuel rail to monitor fuel pressure, and each injector is pulsed for a specific amount of time and the pressure drop of each one is measured and compared to the others. The pressure should drop almost exactly the same for each injector. The test can be explained more if needed, but clean everything up and see if the codes come back.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

https://www.2carpros.com/articles/how-to-replace-a-fuel-injector

The Long Term is more of a learned value that will keep adjusting according to the Short Term. So their comment about it adjusting down is not incorrect, how long it takes depends on how the ECM is programmed to do so. Some manufacturers will be different than others, if its back below 5% either +/- then youre good.

Those fuel trims are just about perfect. You will have to check fuel pressure and see what it is when first starting. Its possible the fuel pump is weak, and has a leak of fuel volume, but can be semi ok once started. I would see what the fuel pressure is during cranking.