why is my 1989 Buick Regal losing accelaration power when im driving it? on 1990 Buick Regal

I have changed fuel pump and fuel filter a couple months back and it ran fine, then one day it started missing real bad , so I changed the plugs and plug wires, I also bought a air filter , and put fuel injector cleaner on it , and now it wont accelarate when im driving it, it hits a certain speed and either stays there or goes, and when you try going up a hill it barely goes, please let me know what you think it might be.

Asked by for the 1990 Buick Regal
1 more answer
could be bad catt or poss defective fuel pump. where did you get fuel pump