Currently, PCR is not required to travel from USA if you can prove vaccination.
However, i would argue that you should get one anyway, from a moral perspective. Proof of Vaccination does nothing to proof that you do not have Covid-19, so you could potentially spread your infection to passengers on your flight and/or family members and friends you visit while in Ireland.
I travel fairly frequently with work. I make sure i have a negative PCR before i return home, regardless of the guidelines of the day. We are at the stage of the pandemic now that we all need to take personal responsibly and do what we believe is the right thing to do.