Revocable vs Irrevocable after death ?

[NaySao]

How do taxes differ for revocable living trusts vs. when they become irrevocable at death, other than the EIN? Interest income, capital gains, real property sales. I just want to make sure I'm filling out the forms correctly. All I know is, the trust was revocable until death and I'm supposed to fill out a 1041.