P0300

What is your question?

i have had a P0300 for a long time. I have changed or checked just about everything from plugs to the fuel pump even tested the injectors and cylinder compression. The first time i corrected it by setting the cmp sensor it was 22% out. Then it ran fine for a short while . it seems to miss between 1200&2200 RPM. Mainly when accelerating and also when cruise is set and going down hill. I have checked every sensor or replaced it. I used to work as a service mgr at a dealership and i even called TAC about it and they could't help me. I left before they could send someone down to look at it. Can you help me ?