1 and 2 are the same for me (although, I don't say amen often, so I usually try to say it like everyone else which varies). But for 3, it's more of uh-mend or uh-llowed.
Yeah after thinking about it some more I can see the difference. I'm not sure if I would pronounce 3 differently from 1-2 or not though. I think I might pronounce "allowed" the same as 1-2 but "amend" a little like you are suggesting.