1)
Why does it say "Ki l'Olam Chasdo"?
1.
Radak: His Chesed will be with us all days of the world.
2.
Malbim: Chesed is miraculous conduct.
2)
What is "l'Dor va'Dor"?
1.
Radak: It is for all generations of the world.
3)
What is "Emunaso"?
1.
Rashi: "Emes" and "Emunah" are fulfilling His promise.
2.
Malbim: It is fixed conduct (perpetuation of laws of nature), like I explained (89:2).