Fuel injector issues
 

I have an 06 stratus, 6 cylinder
It started shuttering on me upon hitting about 3 thousand rpm so I took it into a shop. Mechanic said two of my injectors weren't working properly so he replaced those and it was running fine for about a week then it started with the same issues again. I took it back and mechanic said he checked it and was getting a code for the computer which also ended up getting replaced as well as another injector, again it was running great for about a week or so and It started acting up again. Gave me a code for my number one injector this time, Do you have any idea why it could be having issues like this? Why the injectors would stop functioning one at a time as they are?

Have they replaced the fuel filter?

Has the fuel pressure regulator been tested?