Revision #2: When given the choice of reliving his life, a deceased high-flyer is told by a sagely corpse in order to do so he must correct three past mistakes before his funeral in 48 hours or risk being trapped in Limbo forever.

You are missing an important element which is making the logline a bit difficult to understand.

A: How does he know he must remember his past?
B: How does he know that ‘if’ he doesn’t remember his past ‘then’ he will be trapped in limbo forever.

Because that’s what actually sets the story in motion, not the waking up dead.
==========================================================
Warning: Creative Speculation on my part!

There was a great movie called Switch (1991) where three women who have been scorned kill the man (Steve) who has been sleeping with all of them.

The man, who was decent and generous in other areas of this life, was a jerk when it came to women.
As a result, his ‘soul’ gets transferred to the body of a woman (Amanda– A man Duh)
He is told by?’the powers that be’ that he if he wants to go to heaven he must get one woman to love him.
So now as a woman, he can no longer use his good looks and charm on women he must find a way to get a woman to love him for who he is not his looks, charm or money.

In that movie the lead character had a tangible goal; he must get one woman to love him for him.
and he has an internal journey, he learns to respect women.

In your story, the lead must ‘remember his past’

You should?give your lead a tangible goal
Perhaps the lead character is told by an Angel, When he goes back to his small town, he will remember three past mistakes and has one weekend to fix the mistakes if he wishes to go to the afterlife and not be stuck in limbo.

1: He discovers he wasn’t a good son– He must keep an important promise to his father
2: He discovers he dumped a really good girlfriend– He must fix her up with a good guy
3 Finally, as the weekend is coming to an end, He discovers his new girlfriend is pregnant– He realizes that the insurance money for his death will set his child up for college.
and the best thing for his child to be is to let go…

and in doing so he is released from purgatory and welcomed to Heaven. (or the afterlife)

As he meets the important people in his life, the audience is shown a series of flashbacks which, like a jigsaw puzzle slowly reveal who the lead character was, his flaws, warts and all.

The internal Journey: The lead character was selfish — He begins to understand this as he sees the flashbacks — He becomes uncomfortable with who he was — He does the ultimate unselfish act.
—–
He did not realize he was unselfish when he was alive, but as he sees the flashbacks with fresh eyes (Because of his amnesia) he realizes it.
When he unselfishly gives up his life (Agrees to let go) for his daughter’s?betterment, It is also the conclusion of his internal journey.

He starts out the story with a tangible goal:?fix 3 mistakes, but during the course of his journey he also realizes his flaws and in the end becomes a better person internally.
==========================================================
Thus ends the Creative Speculation